That's half correct, if the BB bounced all the way down, you'd get REALLY bad accuracy because the exit direction would be random more frequently. And the longer the barrel, the more it would bounce, and the lower your FPS and accuracy would be because on a 650mm barrel it would bounce so much that it would nullify your backspin.
It does, however, bounce after it's hits your hop rubber. But it re-centers itself as it goes down the barrel. Thus the idea that a longer barrel increases accuracy.
However as long as you have the proper pressure behind the BB, it can re-center itself VERY quickly, as in a pistol. Thus good compression = amazing accuracy
However the HUGE downside to TK barrels is that there's so much air that goes AROUND the BB due to the huge air channels around it, that it's more likely to bounce around.
I've never had any issues with accuracy, range, or trajectory on smoothbore barrels. Don't need to re-invent what already works great