Most MBA are one of three things:
Charging: there are plenty of ways to boost damage on a charge, so missing out on a little isn't a big deal.
MBA granted by a leader: If a leader is blowing his standard action to give you an MBA, chances are there are some situational considerations. Like you're a rogue with CA, or you're under a buff the leader just gave you or someting like that. Again, slightly lower base damage may not be that important.
OAs and Mark punishment: Here, the point of the MBA is to scare the monster enough that it hesitates to endure it. It needs to hurt. You want all the damage you can get.
So, OK, yes, /some/ defenders - those who don't have strong enough non-MBA mark punishment - may need a strong MBA. And, some of them may not be STR primary. We're talking /maybe/ the battlemind (though they have non-MBA mark punishment) and a swordmage build or two. The swordmage is covered. The Chaladin's mark punishment is nothing to sneeze at, and the Warden's isn't MBA dependent. So, yeah, OK, it might suck to be a battlemind for a minute or two between the reading the errata that nerfs Melee Training, and the one that gives it some other alternative - because they'll both likely be in the October update.