Possibly, but the percentage of youth players that actually make it is so small you just don't know. Garner is definitely a talent but plays a role that players usually don't make their own at a high level until mid 20's. I'd love to see him come through, but for a big club like United we should never not buy players because we think we have young, unproven players coming through.
If Garner is good enough, he will break into the team, if not then so be it. Competition should only be a good thing, the goal of young players should be to develop their game so that they can break through, not United choosing not to invest in the squad and taking chances on young players instead.
Same with Greenwood, Gomes and any other youth players. Bringing them into the squad now might do more harm than good. People always reference the class of 92, but compare the players they had around them vs what we have now. Poor examples and lack of leaders/role models, combined with a team lacking confidence is not a good environment to bring young players through.