My Lilina is a level 12 sage and has less def than yours.
I prefer Lillina over Lugh really. Generally, there's a group of 5 enemies (or so) in this game. Lillina will always take out the strongest one. She isn't very good for soloing though, but I have a few other pairs for that.
Current magic users in my team (at start of 18)
Sophia - Lv 1 Druid
Ray - Lv 2 Druid
Hugh - Lv 3 Sage
Lugh - Lv 5 Sage
Clarine - Lv 8 Valkyrie
Ellen - Lv 11 Bishop
Lillina - Lv 12 sage
Then I have the Paladin pair, Roy, Dieck, Miledy, Thany, Fir, Wendy and Sue as my non-magic users. They're all (save for Roy) in the Lv 1-6 range.
It's a good thing that 7 out of my 15 units can normally heal though :D
I'm always using Iron (and sometimes Steel) weapons, so generally I end up having almost all my good weapons left for the last ~ 5 chapters, making them a breeze. Not sure if that's a good idea.