Yeah, there are plenty of PS options that are really seriously nice. Fighter MC ranger and pick up Twin Strike? Can be very nice indeed. Even better for some other classes like rogue. If you have a nice class synergy and want to drop 2 or 3 PS feats then PMC actually isn't a bad deal. You've already paid most of the cost, why not get the big benefit? And lets not kid ourselves, the big benefit is the full use of the at-will. The PMC power swaps could be nice or not, but there are simply certain at-wills that when combined with other specific classes are VERY potent.
But of course, as you've already pointed out, the whole thing is pretty much just a nerf if you want to do it merely for concept purposes. At least if you go beyond the initial PS feat. Still, it is not all that big a deal to spend 2 feats in return for a skill, possibly a limited use class feature, and one power swap. Even though its only useful once per encounter, that is still a decent amount. The best at-wills like Dual Strike, Twin Strike, and Righteous Brand are really amazingly good powers. Most "concept" MCing is still going to pick one of these sorts of powers, or other ones that can definitely be almost as good in the right hands.
So yeah, if you make MCing cheaper, you just invite the creation of some pretty monster builds. Yet as it stands there are not a lot of cases where you want to go past the first power swap, if that. Still, that doesn't make it a failure. I really don't see how they could have done it better given the rest of the 4e design. Classes in 4e tend to get pretty wonky when you can mix them too freely. Just look at Versatile Master, its insane and pretty clearly broken.