Is the detha-esque stuff champions get akin to raw detha, or is it different?
Would BB training cancel out the champion defense skills?
The only Detha-esque thing Champions have that could really be considered better than what vanilla fighters have access to is a combo trainer (Erthron) that is essentially Evus except more focused on Detha and less on other skills. He used to give a very large bonus, but was later nerfed down to give about as much bonus as Evus does. And, while not really "Detha-esque", Champions don't suffer a movement speed penalty while wearing armor, which comes in handy defensively. But really, a Champion BBer is not going to be able to do much that a normal BBer can't (probably less, since the BB is in its best form when you spend so many of your ranks on it that you have little to spend on anything else), even ignoring the fact that Detha doesn't help a BBer much anyway.
And there's nothing stopping Champions from training the BB now if they want (or any subclass training any specialty weapon), it's just an annoyance to have to switch between trainers constantly because of the rank decay. Seeing as how it's just an *annoyance* and not something that's keeping balance in the game, there should be a way to turn off the rank decay.