It depends, there were a lot of studies that showed prejudice and bias in the meritocratic process. You had examples of CVs with woman names removed getting more callbacks, and anonymous interviews having higher rates of hire and such.
Due to this, people considered affirmative actions to correct for this skew. That would actually make it a meritocratic motivated AA.
And then you have the idea of missed potential. Those who weren't given the opportunity to develop, it limits the pool of exceptional candidates. It's similar to when black athletes weren't allowed in sports. We thought we had a meritocratic process, but we were artificially limiting those with potential. The challenge is bigger here, so you need a bootstrapping process, because you're faced with a chicken and egg situation. You wouldn't know if it works or not unless you give it at least one if not two generations to take effect. I admit that this is the more controversial one, as it means temporarily favoring disadvantaged groups to bootstrap things. I just wanted to point out that there's a meritocratic angle to it as well.
Equity doesn't mean give those that suck a boost. It means give those that weren't given the environment to develop their full potential a chance at it, they may end up being even better than the alternative.