For what it's worth, the most powerful party that I've found so far has actually forgone strength characters completely, but still runs a mix of physical and magical damage. Right now it's an aero/geo tank using wand/shield, a pyro/hydro mage using basically anything that gives good stats, a ranger/summoner, and a rogue/necromancer.
The rationale is that physical attackers suffer greatly from using a one-handed sword instead of a two-handed one, whereas a mage doesn't care that much if they have one wand instead of two. By and large the magical and physical damage sources focus down different targets; however, there's still a fair degree of flexibility (the archer can deal significant magic damage through Summoning without needing any Int; the mage can do a lot of buffing to support physical damage output, etc). Everybody takes a few cheap points in Polymorph for utility schools.
