I’m just a noob in all this Nostr stuff, but from my perception, I believe most users will have/need both: payed relays AND local event storage, just like they currently do with their photos.

I do pay Apple to hold a copy of the photos on my phone, as well as my wife and other non-technical users do, but the Photos app also keep a local copy. 

 If the local relay make a backup on cloud storage (such iCloud or Google Drive) you won’t need paid relay for storing your events