Genuinely I don't understand the issue? You can search the Fediverse from one instance using the Magazines tab in Kbin to find places to sub, or sub to communities you find in all feed etc? Is the issue to do with the duplication of communities at present and lack of clarity which ones are more active?
For me at least the federated set up works well, but I need more visibility of total community sizes when searching Magazines. The search shows me the number of users subbed from this instance, where as I'd also like to know the total number of users subbed across the fediverse to guage how big that community is overall.
Also as you mention, it would be good to see duplicate communities merged across instances - but some of that is the reddit migration with 1000s of new users creating the communities with the same name on multiple instances in a short amount of time. Consolidation will take time (and sometimes there may be a good reason to have two separate communities with the same name) but long term there does need to be tools to allow communities to migrate base from one instance to another or merge; otherwise there is a risk a community could die if an instance falls over.
But I'm not switching between instances - I was initially and realised it was pointless. I have chosen to be on 2 instances - Kbin.social and Feddit.uk, deliberately to keep my UK and generic feed separate for now, and also to have a Kbin and Lemmy experience. I personally strongly favour Kbin at the moment. I don't get the analogy of tabbed browsing or separate forums; you can see the whole fediverse from one instance (barring defederated instance like Beehaw). What am I missing?