Maybe it plays a part but I'm not sure it's the driving force.
De Gea was pretty good last season. Dalot just wasn't the preferred option for Ole. Shaw and Rashford both had terrible seasons.
I think the bigger reason is being in a team where they are properly drilled, playing with better players like Varane, Casemiro, Eriksen and Martinez in particular and increased confidence as a result of this.
In the case of DDG, Shaw and Dalot in particular it must be easier to perform alongside Martinez, Varane and Casemiro offering protection rather than Maguire, Lindelof and McTominay or Fred.
Probably also Ronaldo leaving has helped the team style of play too and Rashford has had to step up now as our key attacker.