Lorenz will never be anything but mediocre. Which is honestly the destiny of most mixed offense units, particularly in this game, due to the skill system.
There just isn't enough room to have the Faires, the Blows, and the weapon proficiency skills needed to he good at magic and physical damage.
My recommendation is drop Lorenz and grab a different cavalier (Sylvain or Ferdinand) to replace him. If your Bylass, Sylvain is the easiest recruit in the game. Alternatively, you can just grab someone like Catherine pretty early and start her down the path of Falcon Knight (Brigand for Death Blow, Peg Knight -> Wyvern Rider -> Falcon Knighy) to replace him as a mobile physical attacker.
Marianne is a deceptive unit. She is clearly set up as the house healer, and she can function in that role since ultimately she does have Physic, but her stats and spell list would really have her operate as a primarily offensive magic user. Raise of faith enough to get Physic, maybe Silence, and then put her on the path to Dark Knight (Monk-> Mage->Warlock->Dark Knight) is easy with her proficiencies. Grab Lindhart or Mercy to make up for your lack of healer because both have a much better faith list. If she really is getting hit by the RNG stick she makes a good dancer.
Im actively trying to recruit Mercedes in this play through. Marianne already has silence for me. I just realized that I havent raised her Reason at all. Its still early so I can work on that. I actually have been mainly working on her riding skills the entire time which explains why she has no reason. Also, Ill drop Lorenz but I dont feel like I need to get another Cavalier. It just isnt necessary. It might be different on the hardest difficulty but that is probably it
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I will admit I'm wrong if you prove me wrong. It's how it always should be