You are making this look far stronger than it really is, thats why i really dont like paper calcs, you go in game group up and wont be able to hit anything on a Kensai because the mechs, barbs, wlocks, etc...have already dropped the mobs in nano seconds. So i guess that leaves kensai with some raid utility? spamming improved sunder maybe...
For design decisions
Gameplay > Spreadsheets
If anything 'power surge' is a nice all-saves buff, which is much needed for a FTR. I'd personally just make it +12 STR, and +4 all stats if 18th core taken, +8 all stats when capstone taken. That would be a nice buff, without the suggestion that one has to MC into fighter for best ability scores.
Id rather have Fighters benefit more from the Fighter cores.