I could use some guidance here - Current team all BT6: Lav / Zephy / Dove / Walla / Fox / Anubis
1) Should I replace him with Lazulix?
2) Should I replace him with Cupid for the buff?
I mainly play dungeons / LR / HBM. Not so much arena / GW.
it all depend which mode you are focusing on.
Since you don't have PD you don't have to worry that heroes will destroy buildings on which he can proc. Therefore sapping Anubis for Lazu is good option imo.
Cupid is not that good. Yeah he can buff damage, but Lazu is one of game changers. If your opponent it frozen he can't attack, and if he can't attack he have problem, and you have huge advantage, which Anubis or Cupid will not give you.
You can give him SL with Empower insignia and it should work without problems in dungeon/raids. For PvP he must have revite 5+