Just crushed grima.
I used a pretty different team.
MaMU
Chrom
Lucina
Cynthia
Sumia
Lissa
Anna
Olivia
Morgan came too late to make a huge difference. Chrom was a decent lord (10)->archer-> sniper, being able to fill gregor's role in tanking (with fred pairups) and plugging chokes in the earlier chapters.
I trained sumia in all those paralogue training missions (and chapter 10 + 12) and managed to get galeforce before ch13, so I could get two aether galeforce children. Turned her into a great knight after to try to get dual guard+ as she can kill someone and then switch back to chrom for enemy phase.
No mire user made chapter 21 a hard boss rush, although galeforce helped in that. A lack of armsthrift (besides avatar) made me extremely poor too lol.
Blessed bow tanking is hilariously good.
Thanks again for the awesome guide! Those chokepoint locations and general strategy tips really helped.