Dweomerkeeper is not broken. I don't see why people keep saying it is. It *might* be broken if you combine it with the Initiate of Mystra feat, which is a FR only feat. Other than that... It is only so-so. And yes, I do have a Dweomerkeeper build that abuse DMM. It isn't that powerful. My Arcane Hierophant fares better.
The dragon thing is a result of the Devoted Tracker feat. Add Beastmaster and Halfling Outrider and stir. Note that it is a very specific build, and you don't have a lot of flexibility to it. You get a 25+HD dragon at level 20. More if you allow the Bloodlines rules from UA. I think the record was closer to 40HD.
TWF is a feat intensive chain. The issue I was trying to raise is that something like DMM precludes you taking feat intensive chains, which restricts you significantly in terms of what you can do with your character. The opportunity cost, if you will. If you are going to sink half your pre-epic feats into something, it had better be worth the effort (TWF as is patently isn't). That is why I don't think that feat intensive chains like DMM are all that broken.
The thing is, most of the "broken" stuff that is bandied around is very specific. If you are going for a particular build and concentrating on it to the exclusion of everything else, then yes, you *should* be more powerful than a generalist. It is not the feat or prc that is broken. It is just someone concentrating on something. A Charger build, for example is extremely ugly, but you don't see people up in arms about charging feats, do you? There is a preconception about DMM that I don't think is fair to the feat(s). As I have said, it is strong, but it is not "broken".
Planar Shepherd, on the other hand, *is* broken.