How so? One of the things that made Wendy so hard to train in the original was that she joined as a lancelocked unit that joined right before a long stretch of almost nothing but axe enemies, making it hard for her to even hit most of them. It's, for example, rather risky for her to engage the pirate reinforcements in chapter 9, who are otherwise useful for training up weaker units.
Cavaliers are already much better than almost everything else, and restricting what weapons each of them can use at base won't change that.
As for Roy's promotion time, I feel that a good spot could be when Guinevere gives him the Fire Emblem (that is, upon clearing chapter 16).