Techroll are not necessarily bad, but the way they are handled in BB removes depth from the game (IMO).
Henkai already said this, but, in most games knockdowns are about advantage. The standing person has a distinct advantage over the floored fool. In BB, there is still an advantage, but instead of oki, we have guessing. As such, the game become more of virtual RPS then it probably should be.
Also, by devaluing a knockdown you remove a layer of decision making from play. For example, do I go for the knockdown or damage?
Plus side of tech rolls is, it makes the game more distinct from other FG's, and it give characters without wakeup options some tools.