It’s tough to say if BB will be more popular than OW even if GBX release after it,
Ya see, I have been giving recommendations to most of my friends who plays FPS (CS:GO) and MOBA (LoL/DotA2) to give BB a try. Most of them felt reluctant to try because they think that Blizzard > Gearbox. Blizzard has huge huge names on them like WoW, Diablo, Hearthstone with huge continuing player base, whereas GBX’s as a brand/name is not that flourished compared to Blizzard. And if you looked into metacritic’s review, BB has sort of a mixed-positive review, but OW has mostly positive reviews from well known reviewers.
The reason I preferred BB > OW is because of it’s content, if I’m bored I’ll go for a few campaigns, and if I feel like owning people I would queue up for PVP. For OW, they don’t give you any story mode, it’s purely PVP where I kinda lost interest in. But that is just my opinion.