If you're not already, use Marcus. He's there to help you in the early-game in order to take hits and dish out major damage to enemy units (using an Iron Sword on him is a very good way to set up enemies for your weaker units to kill them. Later on when he stops doubling enemies you can use the Silver Lance to do the same thing). Marcus's growth rates are bad, so he won't be improving much when he levels up, but don't be afraid to use him. Dieck does something similar when he joins, but that aspect of him falls off earlier in exchange for being a more long-term unit (I know this doesn't apply to you without restarting the iron man, but I wanted to mention it). Other than Dieck and Marcus you don't get a good enemy killer until Rutger--so until then, yes, you're going to have to bait enemies and gang up on them until your units get more trained. Of who you have alive at the moment, I'd put that training on Rutger, Shanna, and Lugh.
I don't know if you care about gameplay spoilers or not, so I don't want to say anything about chapters you haven't played yet unless you state you're okay with it.