Reality and reasoning have nothing to do with each other in D&D. You know that
Really, there are plenty of good manuvers for Swordsages that remain quite useful at all levels (Moment of Perfect Thought anyone? How about Shadow Jaunt?) If you try and fill up with only your highest level manuvers, you will run into problems. Fill up on the useful ones instead.
Regardless, Swordsages were not meant to sit there and dish out an endless stream of damage like either of the other two. This is pretty obvious being that it's the only martial adept class that doesn't have full BAB (and the smallest HD). Tanking is clearly not it's role.