I think I've mentioned why I don't think she's nearly as bad as you believe she is, especially since even canon Archer can barely utilize the actual(already-weakened) abilities of Noble Phantasms without support from Rin.

Really it boils down to "can replace broken weapons quickly, has some magic, also has some last-ditch defenses". It's hardly overpowered. She can't even use the projectile functions unless she actually traces herself both a bow and an "arrow" to load in it, and even if that arrow is Caladbolg II it has to be used from extreme range.

On top of that Flamelord has proven to be quite cooperative and I can easily say something if he does something wrong while using her.