Yes, no, all depends. This debate will continue for a long time but, it all depends on the specific usage.
BH209... for most hunters, they don't need to swab between rounds. I clearly remember shooting 50 rounds and never swabbing between rounds utilizing sabots. I also remember having to use a drill bit by hand to clean out the flash channel quite often, or accuracy would falter. I also remember asking a local sports shop to order and stock more replacement breech plugs because of flash hole wear and again, accuracy falters. I understand that it appears at times it could be "greasy". Cleaning after shooting uses quite a few patches rather Montana Extreme BH209 cleaner is used or Hoppe's.
Now that I'm not utilizing sabots and when shooting BH, it is necessary to dry patch between rounds for two reasons. One loading force and two the repeated accuracy I'm looking for.
T7....... I might just have some experience with T7, specifically T7M pellets. There is no debating T7 causes a crud ring, in some rifles more than others. It really does require patching between rounds. Butch's Black Powder Bore Shine makes QUICK work of the dirt and crud ring. However, I never had to clean out a flash channel of carbon with a drill bit. I didn't need to replace breech plugs after sending 100 rounds. It never appeared "greasy".
Even after shooting EXTREME charges, the rifle would clean spotless with 5 patches.
I can not clean a rifle as quickly after shooting BH209 as I could after shooting T7. I'll use many more patches cleaning BH than T7. My choice between the two..... BH209
All depends ....