It is a tool with a specific job, and the confusion in your gym comes from almost nobody stating what the job is.
A belt gives your abdominal wall something to push against. When you take a breath and brace, you are pressurising your midsection, and that pressure is what makes your torso rigid. A belt does not hold you up and it is not a back support in the sense of a brace — it is a surface for you to expand into, which lets you generate more pressure than you can against air alone.
Everything follows from that, including why both camps sound right:
If you cannot brace, a belt does very little. There is nothing to push against a wall you were never pushing on. That is the honest core of the "learn to brace first" argument, and it is not gatekeeping.
If you can brace, it adds to something real. That is the other camp, and they are also right, they are just further along.
So the question is not your squat number, it is whether you already know what bracing feels like. A quick self-test: at the bottom of a heavy set, can you feel your midsection pushing out in all directions — front, sides and back — rather than just sucking in and holding your breath? If yes, a belt has something to work with. If you are not sure, that is the thing to spend a month on, and it is free.
The honest summary: a belt is a multiplier on a skill. Multiplying zero still gives you zero, and multiplying something gives you a bit more of it.