Yes, I don't think Bontu is that good.
I'd rather have Erebos!
I'd hope that procession will be cheaper than parallel lives. At least once the hype wears off. It might cause parallel lives to drop too, by reducing demand. This effect is probably better in white than in green. I'm going to get one at some point! Zombie Daxos wants it as well as Ghave.
Mentor is likely good in standard/modern/legacy, but not as effective in EDH. He shuts down some combo-decks but won't do much at all to a lot of decks. And, as you say he'll annoy people in multiplayer! I had that problem when I played an artifact-hating enchantment in a game where someone else had a Breya deck - it enraged them and so they attacked me every turn!