Oh, I completely agree with that assertion: Static content hosting is much easier than stateful subscription management, knowing which aggregators to post to etc.
I just think that this does inherently put more work on the subscribers, and there's no real way to do it efficiently in a relatively flat architecture (with subscribers directly polling publishers). WebSub helps with pure distribution, but not with aggregation (e.g. to allow keyword/hashtag search), for example.
That doesn't mean it's not worth still designing a system like that (in my view, the benefits are significant!), but I wouldn't call it a performance win.
but I suspect aggregating / indexing / etc. still is going to be the most resource consuming part of a push-based system if you want your content discovery to not be limited to two-way interactions, which means the gains of a push-based system, in terms of performance, shouldn't be that much (I suspect the main gains will be in realtimeyness instead).
the main point is to separate publishing and distribution, making publishing far more accessible and decentralised. for that to happen, I guess, from a publisher's point of view, the system should be pull based. of course we can have hubs and relays to add pull-based mechanisms to ease the load of the system.
p.s. even in that case, strictly speaking, yes a pull-based system, or even a hybrid one, will always require more work than a fully push-based system.