In fairness to Primal they have no real competition, I mostly use Primal because everything else is worse. Amtheyst I use on mobile, but I have to switch between them sometimes because each have separate issues.

Caching/indexing is a necessity, strfry is the only relay that works at any meaningful scale and it can only do that because its a very simple K:V database. The trade-off with that is its impossible to render a modern UI with simple queries, so clients directly connecting to it get bloated and paradoxically DoS it.

I've got my own nostr app (bxrd) in the hopper I tinker with from time to time but its not a priority.

Nostr is still more open than Ark, its literally just json and websockets, any app can exfil data from Primal's relays and you can DM primal users without a trusted swap lol