Spark - nothing to do with relays. You can use it or not, it's up to you. I don't use Spark.
UX - works for me.
Using my own relay. Use other relays as backups.
ED25519 - these days it does not matter, CPUs are super fast.
Insufficient decentralization incentive - people are as decentralized as they want to be. And they can easily switch relays on the go.
Superior architecture might be true, I don't know, but it means nothing if it has no users. Seems that the users prefer the "inferior" architecture.
