I am using conflict for similar situations myself. I feel like it makes sense for most self-hosted forums to use that attribute, as it's an extra layer of protection. Generally speaking, it's safer to not keep disabled extensions installed if you don't plan to use them again anyway, since it only increases the (slight) risk of a security issue through that dormant and possibly outdated code.
I'm not sure how, but I suppose there must be a workaround for managed hostings that want to provide conflicting extensions. At the last resort they could use a modified Composer client that ignores conflict and replace it with a check in Flarum itself during extension enabling.
Same applies to replace by the way. I've also used that one on quite a few extensions.
