Oh yeah, one more tip for getting streaks to last longer when your characters are still growing that worked for me: There's not a ton of support characters in this game, but it's worthwhile maybe to look through the wiki for them, because I would miss some trying to rattle them off here.
https://skullgirlsmobile.fandom.com/wiki/SkullgirlsMobile_Wiki
But the point is that a couple support characters can take an okay gold or growing diamond and make them strong enough to take on much stronger teams than before. I guess my go-to example for this is the way that Harlequin can beef up anyone that uses special moves, which for me is Parasouls and Ms. Fortunes, and to a lesser extent RoboFortunes. Pea-Shooter does a similar thing with characters that make a lot of shots like RoboFortunes and Parasouls. Combine Harlequin and Peashooter? That's how I really started climbing up the ranks with Primed taking point shooting powered up Naplam Shots and taking advantage of the Critical Mass MA to boost damage even further.
People have mentioned using cheap Valentines with Trauma Center to keep you on your feet, and Surgeon General and Killjoy are particularly valuable for giving you a second chance if you flub things.
Just keep an eye out for characters that can help out your front line people.