THF line isn't that great imho but, whatever. You can still potentially get it with 13 str (enough for PA, Cleave, and Great Cleave - which are way better btw) ad tomes. Loss of PRR... eh, I'll take evasion with high reflex saves, tyvm. You are right about power surge (maybe just 8 levels of fighter I guess, take rogue to 10 for the rogue special feat, more SA and skills) and overwhelming crit (gotta give a lil to get a lil). Also, a dex build would be far far better at stealth if a player wanted to go that route.
Moreover, who is to say one can't simply approach the dex to damage on the falchion as giving archers a viable sidearm if they feel the need to melee? Manyshot isn't up all the time.