Let's analyze this in detail:
Tactics - Decent. Ignoring the silly goals we've conceded lately, we've been excellent defensively & create lots of chances when Pogba plays. The issue is we aren't building towards a philosophy on how we are going to play with the ball in possession and convert that to goals consistently and also tend to shut up shop at the first moment Mourinho loses confidence, which hardly helps. If you've played sports you know that a lot of it is instincts you develop through continuous training or experience. Planning the perfect game & expecting each player to have the intelligence to adapt to any situation is naive & just horrible management in my opinion.
Squad management - The reason we should fire Mourinho or hire a DOF.
FB (questionable) - We had 3 decent FB's (Young, Shaw, Valencia). With Young being able to play either flank, we only need 1 more & probably sell one or both of Blind/Darmian. Youngsters can provide additional depth.
CB (fail) - With Bailly, Jones, Smalling, Rojo, Blind as decent starters & a promising youngsters in TFM & Tunazebe. You could say we can focus our attention elsewhere. Instead we cough up valuable 31m on Lindelof who's not very convincing.
MC (great) - With Herrera playing well last year as the BWM defensive role, we'll need a holding midfielder to pair with him to utilize Pobga, our world class midfielder, in a more attacking role. We buy the right player, but somehow don't deploy them properly as we keep our world class midfielder who can dribble, pass, shoot, hold up the ball, win the ball, head the ball an amazing 40 yards from the goal most of the times (idiotic). Great depth with Mkhi/Lingard/Martial being able to play in that no. 10 role. TFM can sub in for Herrera in that BWM role, Carrick backing up Matic. And Fellaini should be sold, but can be kept as a tactical weapon.
LW/RW (fail) - Arguable the area of biggest need last year with 2 of our natural wingers in Mkhi & Lingard performing poorly alongside an out of position trio of Martial, Rashford, & Mata. We really needed to sell Mata (since we have Pogba & Mkhi who can play that advanced midfield role) & add 2 quality players to which Lingard, Mkhi, Martial can back up.
ST(questionable) - With talent like Martial & Rashford we didn't really need to invest more. Maybe bringing in a cheap experienced striker the likes of Giroud, Defoe, or Mandzukic if we need players who can tap it in. Instead we go spending 75m on the likes of an unproven Lukaku. Imagine if Tottenham would have shoved Harry Kane out wide a couple years ago and bought another CF. Silly stuff.
In summary we have 8 players whose best position takes up 2 positions (attacking mid & striker) in Mourinho's tactics! 0 natural wingers for 2 winger positions. 6 defenders for 2 positions. And not enough depth at the fullback position.
Adjustments & Training - Average. Mourinho tends to learn from roughly half his mistakes, which is a big upgrade from our last two managers. But we see limited improvements in the player's skills or confidence, unless its running around like a headless chicken.
Developing Youth - Not great. Despite an abundance of young players in the squad, they aren't being put. They are thrown in the deep end and if they manage to figure it out great, otherwise they are given the cold shoulder. Hardly nurturing.
Mourinho has gotten the broad strokes right, but has continuously missed with key details particularly with the squad management & sensible youth development (not at the cost of trophies). Not sure trusting him with 200m is wise. Buy 1 quality winger in Jan. & if he can't do a combination of winning a trophy & top 3, replace him in the summer. Too rigid (lack of evolution with tactics), poor motivator (whines & blames others constantly), & doesn't optimize what he has. Only way i think Mourinho can beat Pep is if he buys the title. Why not try and find someone better who fits our philosophy with attacking football & developing youngsters. Klopp, Poch, Tuchel, Ancelotti, & Jardim are some names who can easily do better with the talent we have and the money to back them. Maybe also hire a really good DOF.