The #1 factor has to be the caliber of the manager in managing emotion (energy and focus) as well as tactical adaptation and preparation.
Obviously I do agree, but not with the order.
Tactical adaptation and preparation come first, energy and focus only after that
I am more comfortable with Lenglet moving forward than Umtiti because the the latter's injury situation, is a big older, I think plays a bit more careless, and finally don't think he handled himself well last year with negotiations during a title chase. But I'll agree to disagree about Umtiti vs Lenglet.
So we tend to differ on Umtiti and Lenglet.
Frankly I don't care about any player's push for higher wages or contract renewal. I still have the strong feeling that it's not our business. Players are professionals backed by quite money-hungry agents, and as far as financial matters go, it is not the most complicated venture to misguide a 22-30 yrs old, mostly weakly educated young boy, specially if other renewals happen in the team like a landslide.
Umtiti is good with risky passes forward, which don't always work of course, but he tries them at least. Lenglet is more careful, more of the "Valverde type", but he may improve. I'm not sure as yet.
Nevertheless by watching how easily Salah could fool Lenglet each and every time during the 1st leg, I have the hypothetical impression that it wouldn't have been so easy if the best Umtiti were there.
Lenglet is slow and he will not improve in that regard ever.
Furthermore Umtiti is an exceptional header, though almost as slow as Lenglet is, so a selection is not easy between the two.
Still I have the feeling that Umtiti's potential sale is perhaps not the best idea and more importantly it's not the most urgent change that needs to be accomplished.