I've seen content creators move, it happens over time and they tend to follow oneanother too. Content creators are in friendly competition, so if an app has a feature that helps build engagement, other content creators will jump on it too, and then eventually they will focus on building for the features they prefer.
That said: I expecy the cost to move between apps on nostr to be cheap AF compared to traditional platforms. Most content will be generically supported by all, and then maybe specialised features like merch stores will be on specific apps and people will need to use that app to access it.
Regarding the "one best aggregator app", I use #Amethyst, it is great, but I suspect that eventually many of the features will rot. I already don't use it for accessing streams, I favour zap.stream. Somehow I feel like it isn't as good on #Amethyst.
How things evolve is neither here or there, but at the very least, we should acknowledge, I can still see and interact with you on #Amethyst, even if you use something like #Primal.