How to play RTA

Well I’m not to far into the game, I have been playing since Hecate’s banner and so I didn’t get units like lady of the scales or frieren. So when I play RTA I feel like it’s impossible to win, I’m always getting out sped and I’m not sure what to do since I don’t have the widest range of ML characters, I got a few recently but sadly they are kinda outdated I think like top model luluca, ML Ken and straze so any thoughts or tips to help me climb or just get better??