I often see sequential order IDs, and they get incremented by one, so I can guesstimate the amount of orders they get within a minute by creating my own orders. I watched this happen as I was intentionally removing and creating new orders (as they did not support modification of existing but not yet accepted ones). What may I do with this information though as an user that would be damaging? Legitimate question, intent is not harm, but I genuinely do not see how this is a bad thing.

I can see it being bad for tracking IDs, but not order IDs, unless you are allowed to view any orders that do not belong to your account, which is just fundamentally bad security and using UUIDv4 or a random string would simply be obscuring security.