No, your solution isn't a good one. For one thing, the game doesn't always know which piece of gear is better than another one, so there's no guarantee they'll equip the best one. Just look at the crafting components and see how many low tier components have better stats than high tier ones. Also, if I want to train my spouse as an archer, its not necessarily because I need an archer, but because I believe they'll be safer as an archer than a melee cavalry, and that's my prerogative. But if, say, they have higher skills in throwing weapons and polearms, they won't equip the bow I give them.
I don't know why you're so concerned about stealing spouse gear in the first place, tbh. Its your spouse. Your stuff is theirs and their stuff is yours. I don't see the problem here.