Personally, I'm there with you I think. I only use default web-UIs on all fediverse platforms I've used, and advocate for that.
But should multi-protocol systems and multi-platform clients become normalised, I think this goes beyond "to app or not to app". What I'm talking about could likely just be a web-app.
The issue is more around aggregation and creating something "greater than the sum of its parts" out of open alt-social.