Here's my stats from 18 and 20. I know they're not the best, but I don't think they're that far off what you've got.
I think there's only the two magic users in the chapter, right? Two in the middle, two on the top right? Once Leah dunks on all them, you should find tanking a lot easier.
And yes, I know my Renfa is kinda busted. But I think she's the only big exception.