Normally? Yes, such questions are on-topic and (often) work within our peculiar site structure. It really depends on the individual questions though, and questions are judged less on rules and more on their individual merits relative to broad guidelines.
This question in particular isn't a typical example of conversion questions, as it has several small problems that likely added up to a collective judgement to put it on hold:
It's not well-researched. Dungeon World already explains how to convert monsters, and the question itself says that reading the classes to see if they already work hasn't been done.
Lacking research ahead of time isn't by itself grounds for closure, but it sets the question up as particularly weak and therefore less likely to be “saved” by community action from any other problems it might be suffering from.
Asking about both monsters and all the classes is kinda broad. Whether it's too broad or not isn't something we can define with a clear rule, but that's why voting is used instead, to judge more effectively on a case-by-case basis.
In this case, explaining how to convert all the classes and how to convert monsters in general makes for an unfocused question. That alone might not get it closed, but it weighs heavily on the question's overall evaluation.
Normally such a question would be expected to be split into two separate questions (one for monsters, one for classes), but the problem in (1) mean that doing that might not be useful anyway, again making a hold — to give time to sort things out — more attractive to the community in general.
The question asked and the underlying problem seem to have a mismatch. The motivation for asking appears to be wanting to know whether Dragon Warrior classes and monsters have been made for Dungeon World yet, but the question is asking how.
This adds to the general sense of being unfocused, or suggests that there's more going on behind the question, which will make it more likely for focused answers to miss the “real” target the asker is hoping they'll hit. Hold/closing is a way to head off the posting of answers when it seems likely they won't even be answering the real question.
There seems to be yet another question asking whether Dungeon World can do low-magic campaigns, buried in the middle of the question. The more questions a question-post appears to contain, the more likely it is to attract Too Broad votes.
Lastly — and this is a really minor point that wouldn't merit a single hold/close vote, but contributes to the sense that there's something wrong with the question that needs to be fixed before it can be usefully answered — it refers to itself as a “thread”. It also expresses a hope for general feedback from people.
RPG.se is frequently mistaken for a threaded discussion forum but works very, very differently from one. Calling a question page a “thread” or seeming like an experience poll are each a very minor red flag that the original post might have been composed under misapprehensions about what would happen next, based on a belief that this site is a typical discussion forum. Again, not close-worthy, but it's one more thing weighing down a question that is already weighed down with a number of warning signs of being not ready for answering.
The close/hold vote system is really granular, and doesn't really allow expressing every reason, doubt, and intuition that it relies on voters to use to make their judgements, so the overall reason “Too Broad” is often good enough, but sometimes (such as in this case) not anywhere near the full story. It falsely gives the impression in this case that there's one specific axis of problem when it's really many things, and “Too Broad” is just the closest match for the build-up of small problems.
These problems aren't insurmountable though. There are a few things you can do to move forward:
Take another spin through the tour for a review of how RPG.se works in a way that is distinct from a discussion forum.
Finish reading Dungeon World. It answers one half your question already (how to convert monsters), and finishing reading about the existing classes may solve the other half.
If questions remain after (2), keep in mind that questions get better answers when answers only have to answer one question. Ask specific questions about specific problems by focusing on one task that you're having trouble completing.
Along with (2), this ensures that the question will be written with one clear hurdle that you're having direct trouble clearing, which answers can laser-focus on solving for you.
Decide which question you want to ask about first — the other questions may be moot by the time that first question is answered.
If you finish reading DW and still want to know if Dragon Warrior classes have been already converted to Dungeon World by someone else, just ask that. If you finish reading and determine that you will convert them yourself, then you ask “how” and stay focused on asking “how” while writing the question. If you want to know how to do low-magic campaigns in Dungeon World, ask that all by itself. (You might not have any of these questions, and may instead find yourself having a completely different or more specific problem.)
This goes hand-in-hand with (3), in that it ensures each question post only contains one problem to solve rather than a muddle of many problems that could each be individually solved or ignored by any given answer.
