It's positive but it didn't sustain. Progression spiked and then dipped. His poor transfer record meant that he didn't build a team that improved over time. He was sacked because it wasn't going well. United, as a club, have built a legacy on sustained strength and dominance rather than sporadic cup success which can be achieved through nice draws and occasional decent performances.
The only way you could say that a United manager had a massively positive contribution, based on the club's supposed standing, is if they have genuine title challenges over a series of seasons (Jose had none) or they rekindle top European status (Jose didn't). Based on that fairly reasonable criteria, I would suggest that his contribution was positive for a while and then dropped off a cliff. No legacy of anything positive.