I don't think it's weird. Right now it probably isn't great cause the pool of commenters is already small, and this dilutes it further, but I think in a world where we had plenty of people in all those communities it would be fine.
It does suck on the posting aide, though, and it also seems like there might be some use to a tool/feature that merges them somehow so you're viewing it all together and respond to whoever you like in one place.
I said this a while ago on another thread, but if I was a Dev on the project I would be working to create a website that automatically signs you up for an instance. The high level concept is instances would opt into this pool, the user would simply put in their username like any regular website, and then the system would create them an account on whichever instance was best for them (maybe based on ping/trying to spread population around).
This would majorly reduce the barrier to entry in my opinion, because a lot of people just want to browse, and don't care about the federation aspect at all.