While OP has a point regarding a potential problem, the term ‘fundamentally broken’ is an absolute overstatement. At most, it could be stated that Lemmy/kbin might not be feature complete yet. And i expect, given the crowd sourced nature of it, that it will dynamically evolve into our users combined needs. No need to abandon it!
Now about the actual point: as others have mentioned, the way Lemmy handles multiple subs on same topic on different instances is good. The communities are easily differentiable via the instance prefix, and if i want both, i can simple subscribe to both, and will see the posts from both in my feed.
I don’t like the tag idea, because such global consensus about what e.g. a horse is might work for a horse, but not for other terms like ‘politics’, which would depend on the jnstance. If i see a politics sub on an italian instance, i expect it to be mostly about italian politics and related world politics, which is good.
Great. There seem to be two ways to donate, Patreon and OpenCollective. Is one better than the other for the devs regarding fees? Afaik Patreon claims a small fee, not sure about OpenCollective.