I don't really believe this. It seems to give you a second slot for a weapon drop, which you will pretty much fail all the time.
Is double the chance better? Hell yes it is. Is double times nothing impressive? Hell no.... and even with Awakened base 15%, you're still not at 100%, despite using a... what is Fluffy's uptime, 2/10? So Avalanche is still stronger than Barrage (during those few turns, even). And even if you go above 100%, the drop in burst generation is extremely small.
The entire "Double+ is bad" meme really, really, REALLY needs to die. Seriously. Let's end it.
While technically possible (for example, Tish can make you hit 100% combo after which Double+ is effectively Triple-), I do not see a realistic team where Double+ would actually hurt you. That would require running multiple Tish or Brahma style characters while still maintaining a functional team. While I have no idea what kind of Hime we're getting in the future, I don't see it happening.
So really, all you're doing is confusing a new person to the game with needlessly unrealistic and niche scenarios.
But yes, the Bow is awful since it doesn't have Assault.Even at full HP, your Assault*Vigor would be 2,368 (which drops down to 1,924 at 83% HP, so basically when something glances at you). 9x FLB Assault weapons (not even Assault++, but Assault) is 2,35 modifier. You're basically asking if it's smart to replace reliable Assault with unreliable Vigor. What do you think?
Since I doubt that you have a full FLB Grid though, it is difficult to say what is the "correct" (and by that I mean realistic) Grid for you, though.
But as for Vigor, unless you're fighting content which simply CANNOT hurt you (see: previous Skill Checker-kun), Vigor is something that you only splash into your Grid, as a yet another modifier it can be hugely helpful. It is NOT something you center your Grid around. This makes Assault/Vigor weapons VERY impressive, but Vigor-only Grids really just make your Grid unreliable.