Mesprit's lead set should probably be changed to something like this (and also moved to top):
Mesprit @ Expert Belt / Leftovers
EVs: 120 HP / 252 SAtk / 136 Spd
Modest Nature (+SAtk, -Atk)
- Stealth Rock
- Ice Beam / Grass Knot
- Thunderbolt / U-turn
Speed is enough for Timid Omastar leads, BoltBeam abuses Expert Belt to the maximum and hits pretty much all leads Grass Knot do, while retaining the ability of dealing with things like Moltres, Grass-types, opposing Mesprit and whatnot. I left Knot and U-turn slashed in case you want to use Mesprit as a scouter, as Grass Knot suffices to check things like Cloyster and Omastar (which are the mostly concerning leads anyways, as they can spike on you). Leftovers can be used with U-turn and Grass Knot since you OHKO Omastar and only max SpD Cloyster has a chance of surviving (and even then it's probably just switching out).
Gonna take a second look later (kinda in a hurry right now), so for now that's what I could think of (perhaps put back the CB set, doesn't sound too bad in theory but I don't know).