Cristiano Ronaldo improves any team, even at 36 he's still one of the best players in the World so yes of course he improves them. The issue with United, as Souness, Carra and Neville allude to is wider than Ronaldo. Ole is trying to deploy a high press system with a selection of players who are not carrying out the game plan, that's the issue.
So either the game plan needs to change (i.e. not high press) or you play guys like Cavani alongside Ronaldo to deploy the game plan. Add to that defensively United are a mess, and you're not winning anything with guys like Mctominay and Fred in your midfield - that has always been a massive hole for them.
Ronaldo has literally won them 2-3 games already this season and by all accounts was the only player yesterday who looked like he gave a shit yesterday.