Why it's painful
Alolan Whip (AW) will be your worst nightmare if you're a player who loves...
- Shielding (to punish with grab, aerials out of shield, etc.)
- AW is a command grab, so it'll get you through your shield, as I'm sure you've found.
- Spot dodging
- This is actually not a good or reliable option--regardless of your timing.
- Dodges stale, so depending on how much you've been dodging and how big your character is, it may be impossible to spot dodge AW.
What are the weaknesses?
Incineroar's biggest weakness is his approach. He has very slow walk/run/air speed and no grounded attacks that come out quickly. The only option he has to make approaching easier is AW.
But even AW has a bunch of drawbacks. It's relatively slow and has a lot of end-lag. If it doesn't land, you'll very easily be able to punish it. Hard.
So what should you do?
It sounds like when your opponent approaches you, your instinct is to turtle up in your shield. Break this habit! It can be great for certain matchups, but especially against Inceroar, this is your worst possible option.
Instead, work to build some other options into your neutral game. That could be things like...
- Dashing in and back out to bait options like AW.
- Short hopping when the opponent approaches to punish.
- If you find AW is still catching you when you do this, throw a quick aerial out when you short hop. For all the characters you play, that can be nair, which'll stuff the AW out (AW--because it's a grab--has very low priority)
- Full hopping over when the opponent approaches to gain stage control and reset neutral.
Alternatively, you could change your play style entirely. Instead of turtling up, you could...
- Play aggressively (playing a rushdown character here will help, but you can still play rushdown style with Terry).
- Be the one to initiate in interactions. AW is very difficult to use from a defensive position
- Play a zoning game (playing a zoner will help)
- All three of the characters you play have decent projectiles. Use them! Incineroar in particular will have trouble getting in if you wall him out.
TL;DR/Conclusion
Incineroar is very slow, so playing passive is the worst thing you can do. Be more active! Try other options like dashing around, jumping or changing your playstyle to put some pressure back on the Incineroar player.
While AW feels impossible to counter, this is only a result of the turtle playstyle you're using. Work on incorporating some new options into your gameplay!