Growth improvements are something that can be said to anyone in Binding Blade since that game structures more as a base > growth game most of the time.
Bases for some units apart from Roy is also necessary.
However, it really is just needing to make his promotion be in Chapter 16/16x, rather than 22/22x. It's so late in the game that it's stupid.
As a character, make Roy be more involved. He's just there as the leader of the army, but he by no means feels actually involved. Lilina has far more involvement than Roy does since it was her father that was killed, her kingdom that was betrayed, and so on.
The perfect way is to actually show and depict how Roy truly learns about how there are humans that do terrible things but also see the good. Roy should serve as the foil for Zephiel. Where Zephiel was estranged from his father's assassination attempt that he believes all humans are evil, Roy has to see the good in humans to say that they deserve to still live through.