Are oozes overpowered for their levels due to the Engulf ability?

Question

Background

Early in my campaign, there was a combat encounter where three level 2 PCs fought a single gelatinous cube. The cube was the standard level 3, and there were no special outside circumstances such as difficult terrain. As per the XP reward and XP budget rules, the cube was worth 60 XP, a Moderate threat encounter for a party of three. The cube proceeded to kill a character and another character's animal companion.

This week, much later into the campaign, three vaultbreaker oozes (level 6) engaged with a party of four PCs (three 7th level, one 6th level). The PCs were at full health, had no afflictions, and had nearly all of their spells available as this was the beginning of the dungeon. Again, no difficult terrain or extraneous circumstances. Based on the XP reward and budget rules, the encounter would have been worth about 90 XP, a high-moderate to low-severe threat encounter. The oozes caused a total party kill.

The Apparent Cause: Engulf

It seems to me that both of these deadly results were the direct result of the Engulf ability. All deaths occurring from the two aforementioned encounters were the result of accumulated damage from acid and suffocation resulting from the oozes' Engulf usage.

Some things to note about Engulf:

• The ability is unlimited in use. There is no cooldown. An ooze can use it every round (and it seems likely that oozes would, based on my interpretation of oozes' main goal of mindless consumption).
• The ability only costs two actions and is not itself a Strike, which means a Strike can be used before or after Engulf at no multiple attack penalty.
• The ability doesn't require the ooze to move in a straight line -- it merely states that the monster Strides up to double its Speed, meaning that it can turn and twist during its movement, allowing it to effectively "roomba" up a large area by sweeping itself around.
• Creatures can Engulf as many creatures as can fit in their space. So large oozes like the gelantinous cube and vaultbreaker ooze can Engulf up to four small or medium-sized creatures simultaneously.
• Engulfed creatures are pulled into the ooze's body and are grabbed, which I interpret as meaning that they remain in the ooze's body as it moves, including the continuation of the Engulf's double Stride.
• Though the Engulfed creature can attempt to escape, it is Slowed 1 by the Engulf, leaving it only two actions to do something that may be quite difficult for physically weaker characters.
• Engulfed creatures are subject to suffocation rules.
• Casters are unable to target Engulfed PCs with spells like Heal, even if the ooze is translucent or transparent.
• From what I can tell, someone else can't Rupture you out of an Engulf. It has to be the Engulfed person performing the Rupture.

Some things to note about oozes:

• They often have large HP pools, meaning it's tough to kill one quickly if it's Engulfed your ally.
• They are immune to critical hits, so double damage isn't applied even though crits happen often with oozes' typically low AC.
• They are mindless feeders, so it's hard for a GM to come up with a reason that they wouldn't finish a PC or party off -- assuming the PC or party hasn't been engulfed before or after the PC or party was defeated, which probably would be the case.

How It Happens

1. The PC is Engulfed.
2. The PC takes acid damage from the Engulf at the end of their turn, every turn.
3. The PC can't breathe and is subject to suffocation.
4. The PC eventually hits Dying 1. At this point, the PC can no longer hold their breath since they are unconscious, and therefore become subject to suffocation damage if they weren't out of breath already.
5. The PC's next turn ends, at which point the PC hits Dying 2 as a result of the acid damage, and possibly Dying 3 in the same turn if the PC fails their fortitude save against suffocation.
6. The PC saves against death, possibly dying.
7. If the PC survives, they can gain another 2 points of Dying easily next turn due to the acid and possible suffocation damage.
8. And so on.

As you can see, the combined effects of Engulf can quickly kill. Suffocation is pretty deadly as is, but Engulf takes it to a whole other level.

Are oozes improperly balanced, or am I doing something(s) wrong?

It seems to me that oozes' threat is far too high for their given levels. Am I running oozes wrong, or is this a balance issue with the system?

ADDENDUM: As a wise commenter pointed out, the third option is that my players are simply suffering the results of not treating oozes as the special case/danger they are, and should have taken special precautions against them (especially since my players have 15+ years of gaming experience and knew the dangers of oozes in both Pathfinder 2e and other systems). This is a definite possibility, and I'm happy to receive answers related to this.

Answer 1

Party composition, size, and tactics are to blame

Funnily enough, I have a party that has fought oozes twice and very successfully. They too fought a Gelatinous cube, and against a trio of Living Saps when they were level 6. Here are the problems I can identify, which I'll compare to my party's experience for reference:

• Your party had only 3 PCs in the first encounter. This means any effect that takes a member out of combat (i.e. Engulf, Paralyze, etc.) is going to be more powerful than the normal 4 person party - it takes out 33% of your capabilities and actions, not just 25%! My party has had two ooze encounters with 5 party members, one against multiple oozes (Living Saps). One of them gets engulfed and they only lose 20% of their actions.
• Your party member has only one martial... and it's just a rogue in the only case where you had a good party size. Hopefully they weren't the under leveled one too. This means that you'll really lack consistent damage against anything with immunity to precision (or perhaps damage at all, if none of the casters has gone the blaster route). It also means you lack someone who can really take hits on the front line. It's no wonder they struggled to escape; they can't do the damage needed for rupture (a non-Thief or Ruffian rogue would struggle with this too), and they are probably not prioritizing the skills needed to successfully Escape (Acrobatics, Athletics, unarmed attack mod). My aforementioned party has 2.5 martials (a Warpriest, Fighter, and Thief rogue), and both the other casters have a high Acrobatics.
• Why are your spellcasters so close to the ooze to begin with? Ooze's have hardly enough intelligence to "prioritize the squishies"; a Gelatinous Cube has only 15ft of movement, so if you are 50ft away, you are totally safe! Lots of spells work at that range. Let the martial put themselves in danger - that's their job. At more than 60ft, the ooze can't even see them. While my party's Gelatinous Cube encounter was in close quarters, they spread out (not really intentionally tbh) and the ooze could only get to them one at a time. The Living Sap encounter the casters kept well away from the cubes (they were outdoors so it was a bit easier to manage).

Sadly, only one of these things is easy to change (tactics), and that could be negated by being in a small room. So I'll offer this general advice to your party:

• Hero points? Are they using them? Are you giving them? Rerolling those saves to avoid getting engulfed is sure helpful.
• If more oozes are going to be a thing, you might want to give one of your caster's Sudden Bolt. Fights versus one ooze tend to be a race to the finish line, as far as damage is concerned, and that spell helps a lot with that.
• Your party should look at getting another martial. They have no front line to keep bad guys off of them, and even their martial seems squishy.
• I would be cautious about having underleveled PCs. A single level is roughly a +1 to +3 difference on everything (the +3 from a proficiency increase), which means an underleveled PC can be severely handicapped, especially in comparison to Pathfinder 1e or DnD 5e.
• Make sure your party is taking time to refocus and heal up between encounters; nothing you said indicates they aren't, but this is a common enough issue that gets overlooked.