What I see as the core problem of BGs
In my opnion, BGs aren't a bad mode per se, but a combination of two aspects makes it a painful experience.
1) losing matches pushes you down
This has been discussed a lot, so I won't talk about it too much. This generates pressure and makes any loss frustrating.
2) the matches are insanely long
This itself wouldn't be an issue, but in combination with the first problem, these two synergise to create a terribly stressful experience. Not only do you lose energy and progress whenever you lose, but the time investment required escalates really quickly. A match usually takes around 10-15 minutes, which is honestly pretty long time.
Unfortunately I don't have a solution for this, but I feel like these two aspects are the core issue with BGs. Just saying that if matches took 5 minutes, I don't think I would mind losing nearly as much as I do now, even at the cost of reduced rewards