An 11"-long permanently fixed barrel would make the blaster awkward to handle. There's no way I could load something like that while the blaster was still mounted on my shoulder, even with my freakishly long arms. Just putting the dart in the end of the barrel and holding it in place while priming would be a challenge.
Angel's had what I refer to as a "pull-out" breech, if I'm reading it correctly, whereas mine is vacuum-loading. So mine has better RoF but worse range.
So no, I don't think making a PAS vacuum-load would lead to a higher RoF than a breech. In fact, I suspect it would be just the opposite. Wouldn't it have just been easier and more practical to use a coupler and a speedloader?