It's good, but the fights are shit. It has luck involved where some hits land and some don't which makes no sense. I got boosted 5 times and still died. My stats were like 3x theirs but they could still hit me and take chunks out of my health. It's like if Luffy fought Goku and actually managed to not only hit him but damage him as well even though that would be impossible. So I can't play this when there's no good way to grind stats before these fights. If it gets added in, I wouldn't want to start over just to get better stats either.
It's not entirely about luck, you need to learn what each stat does. Agility is what allows you to hit and dodge, with defense also playing a big part but only for melee physical attacks, the tooltips in the phone status should explain all of that.
So, unless you're severely underlevelled (which I don't think it's possible, you should still have 400-500 on each stat), you might try doing promotion to knight, then boost.
If you cannot boost before you get killed, you can promote to knight, checkmate, promote to queen, then you'll have enough mobility to run around while you maximize your boost.
But yeah, battles are entirely optional. Also, the training methods that'll get added in will be retroactive, so no need to restart.