For my campaign world I think I could happily rationalise this... of the two monks at 10th level, one focussed on his martial skills, while the other his spiritual essence. although the Mnk10/Ftr10 has a slightly better attack for his top two attacks, he is only doing 1d10 per blow, compared with Mr Zen who is doing 1d20...
The most optimised for damage and attacks would be Mnk16/Ftr4 who could get +16/+13/+10/+7/+2 for 1d20+2 (unarmed specialisation!). He would be giving up timeless body, slow fall, empty body, perfect self and speak with anything living for 3 combat feats - a tricky decision to make IMO since those are some kickin' monk abilities amongst that list.
Interesting.