I jumped around on b6 for a bit.
-I could be wrong, but this map seems longer than any map currently in the competitive rotation. There's probably a reason for comp 6s maps being generally around a certain length, but I couldn't tell you why. I speculate that it has to do with how fast respawning players can get back to an ongoing fight.
-If you want this map to make it into the competitive rotation, comparing it to cp_granary might be helpful, since I think this map is somewhat similar. A lot of people hate cp_granary for various reasons, with "too many tight choke points" being a major one, since it makes stalemates more common. For that reason, I might look into widening the entrance and/or removing the ceiling of 1 or 2 flank routes in total between last-2nd and 2nd-mid to allow for more fluid play/make sacrifice plays easier for both teams. The transition between 2nd-last seems especially chokey, since it's just the dropdown and 2 tiny doorways.
-I keep hitting my head on the ceiling arches on last and 2nd when jumping around; this might just be because I'm not used to having curved ceilings when jumping around comp tf2 maps and need to git gud. I would say keep them for now, but be sensitive to feedback.
-The cap area on the 2nd point is pretty big, bigger than most I've seen. Would need to see this in some sort of competitive play to give any judgement on whether that's good or bad though.
Edit: Made my formatting much easier to read