Crossing is just an aspect of passing. Heading is mainly just an aspect of scoring. Weak foot isn't even a category, it's just an aspect to everything. Yet when someone can't achieve with 2 feet what another can do with 1, then that isn't being more complete.
It also doesn't all weigh the same. You can't look at someone being a crosser, and one being specialized in through balls and claim it's even.
A through ball literally sends an attacker into a 1v1 with a 80% scoring chance, and a cross is total inshallah.
Messi is the better shooter, the better passer, the better dribbler and just as shit of a defender. Which would make him more complete than Ronaldo. Ronaldo can maybe play a pass with his shoulder, or his back, or jump high, but if the sum of all it's components is still lower than what Messi does in a simpler manner, then he isn't more complete at the relevant parts of the game.
Messi with his apparent lack of abilities still managed to outscore and outassist CR who supposedly has this perfect toolbox of a body at hand.