So, after running some numbers, I have come up with a rough way to calculate stats of new mercs.
Take the base stats of the Epic 4-star merc and multiply it by 4.041 to get the fully evolved (no crystals) stats.
Works for MX Sentinel, Repaired Cyclops, Bionic Smasher, and Restrained Titan.
Raid Boss: (ATK based skill)
Event Rare: (AGI based skill)
14463.03119 <----OPE200 would have over 15100 AGI