This probably belongs in the Forge, guys.
I only played BA briefly (with proxy models), so take what I say with a grain of salt. To me it isn't all that important that BA have access to generic marine book options. There's no reason for them not to have vanilla marine options, but if you want to build a list around hunters/stalkers, thunderfires, and grav centurions, you can just use the vanilla marine rules. You can still paint them red, but you aren't missing out on much aside from the chapter tactic at that point (and several other chapters are arguably solid replacements for them anyway).
To me, the whole point of giving BA their own book is to support a measurably different playstyle. In 5th edition, that playstyle was all jump packs all the time. Which was cool. No other marine army did that (or at least not well), and your BA-specific units such as Sang Priests supported that. Now days, BA don't do jump pack armies all that well. I mean, you still do them better than most, but that's not saying much. Sang Priests are frustratingly unhelpful/rare now, and assault marines aren't troops.
So if we're tweaking BA, the first items on my wishlist are to move assault marines back to troops and to do something with the sang priests (maybe make them an attachable character tac and assault squads can take?) to make them more prevalent. Lots of sang priests jump packing into action with their assault marine and death company buddies isn't bad, and your chapter tactics actually look pretty good on paper (to me). The army has simply lost its overall cohesive theme. Rather than being "jump marines," they're just normal marines that stab slightly better (who cares when you can't reach assault reliably?) and lack a handful of the newer/better toys.
And to boost scouts and dreads to be inline with the newest marine books.
There's a good argument for rolling BA and SW into the generic marine book, but that's a whole other discussion.