They "commit roster space to a less talented player" because he's the most talented player they have access to, to fill a need for a bench player capable of filling in at multiple infield positions, including SS. It's not a wasted spot. And the fact he IS a less talented player means he's not going to get as much playing time as Polanco. Not nearly as much, no matter who went 2 for 3 yesterday, or 0 for 3. Nor should he. You cant just let Adrianza get 600 PAs to confirm he's not as good as Polanco. You already know that, or at least believe it strongly enough that no manager is going to take those 600 PAs and willingly give them to Adrianza. Or any other backup. Which isn't to say you dont need backups, of course you do.