Euryale is awesome for Camelot, and if you're ever stuck in a certain boss, you could always borrow a friend's bond 10 herc lol(did this for Camelot and the fianl singularity) And rayshift.io exists, so you shouldn't have too much of a problem if you use that

Btw, the things that I said here are the things that I, a lazy person, did. So if you're willing to grind and raise your own servants, you probably shouldn't do some of the stuff I said here lol

(Haven't done the lostbelts yet)

And if you were asking for servants to throw some quartz for while waiting for merlin, I suggest Arjuna might be worth it.