Why every build here is a mixed one
On paper casting wins. Magic is the least-absorbed damage school on 44 of the 85 enemies and bosses that carry absorption, averaging 19.2% against physical's 25.4% — so more damage lands per cast than per swing, most of the time.
In a fight that is only half the story. A cast has a wind-up, and a gang of enemies on top of you does not wait for it — at melee range, swinging is often simply faster than casting. That is why all four builds below fill the same three slots: both hands for melee, and the third for a crossbow, a throwable or a catalyst, whichever extends what the build is built around. A caster with a weapon it is not worth swinging has thrown away a slot.
The arsenal says the same thing. 147 of the 218 weapons in the game require two or more offensive stats before you can lift them, and the best of them scale on both — Ravager Gregory's Sword is A+ on Strength and A+ on Radiance at once, and asks for 30 of each. A pure spread cannot hold it. Three of the builds below are crosses for that reason, and two of them out-damage the pure build they are crossed from.
The absorption and requirement figures are read from the game files. The reason mixed loadouts win in play is experience rather than a number in a table, and it is here because our own arithmetic would otherwise point somewhere the game does not.
Or build your own
The build planner takes any stat spread and ranks all 218 weapons for it, including rune effects, and encodes the whole build in the URL so it can be shared or bookmarked.
These pages and the planner run the same calculation, so their rankings agree.