This is a bit disingenuous since few of the issues we have, in terms of defensive shape, stem from his desire to stretch the pitch with as many as 6 players in the attacking third. Mourinho-ball was never about that. His motto is "attack with as few players as possible and if that doesn't work, have certain players to join the attack from the second lines". The last time he managed to pull a rabbit out of the hat like that and showcase his "tactical brilliance" was back in 2015, when he used to overload the left side and then have Ivanovic joining in the attack from RB. All things considered, Solkjaer is far more courageous than Mourinho with the general positioning of his players when United attack in full stretch.
But, this is about the how. If you're talking about what we are trying to achieve on the pitch, the truth is that not much has changed. We still want to be as direct as possible and instruct the forward and the wingers to always look to exploit the spaces in-behind the moment we clear the ball in our third. We still don't perceive possession plays as a way to establish control, but only as a means to inviting press and, subsequently, opening up spaces behind the defence. And we still overload one side to switch play as the best way to move the ball forward. In this sense, little has changed, and it comes as no surprise that some problems in our game from Jose's time persist today. The forwards make the early runs and they create pockets of space between the lines, but nobody moves in to occupy them. The lack of any meaningful possession game often kills all rhythm and tempo. Finally, switching sides when there's absolutely zero vertical movement off the ball is nothing more than an exercise in futility.
Something similar is happening with the midfield. People accuse Solsljaer of cowardly tactics, when the simple fact that whoever we pair in there are asked to perform beyond their capabilities is clearly what's at fault. It's true that Mc Fred were rubbish yesterday, but there's a reason they are considered our best choices in the centre of the park. The area of responsibility is huge. And when we're on the ball, our hastiness to be direct and the lack of involvement from the attackers in the build-up often creates a frustrating sight: When our midfielders are on the ball, their teammates move away from them (or stand still in advanced positions) instead of making themselves available. It's not working and would not be working even with Kroos/Modric in their place.
Speaking of Kroos/Modric, let's look at how Zidane became a success in Madrid. He sacrificed an attacking midfielder to force Casemiro down the throats of a fanbase who only want to see their team play with style. And when Bale was underperforming, he took him off in favour of a midfielder (Isco) and reverted to a diamond. Hardly the most attacking of changes, but they allowed Real Madrid to become a more balanced side.
And trust me, Conte would never dare to leave the central channels unprotected. He would think of playing Pogba in there, but only if he knew that the odds would be in his favour in the long run. Just as Matic/Kante were his go-to pair at Chelsea, but he would also deploy Fabregas as a deep-lying play-maker quite often because he was fine with route-one football too. But he did all that with Costa leading the line: A forward tailor-made for this type of football, able to play with his back to goal, wrestle with defenders, keep the ball and chase it like a rabid dog. Not with Tony freaking Martial on 250 thousand quid p/w or with the 37 yo version of Ronaldo. Also, unlike Mourinho, with the patience to help Lukaku improve at Inter.
Going back to Solskjaer, he seems to have backed himself into a corner. He has created a top-heavy side with many forwards who like to rely on instinct and contribute very little in other areas. Thus, the overreliance on Bruno to orchestrate the attack on his own. Then, Solskajaer understands that we have to take better care of the ball (remember him and Mckenna gesturing Bruno and co. to slow down and pass the ball around?). But Matic can't run any more, VdB is not fit for a physical battle and Pogba is a defensive liability... Well, managers are being paid to find solutions, not to ask for transfers all the time. Change the set-up: Matic is the only holding-midfielder you have, so make his area of responsibility smaller. Beek's short-passing can be crisp, so create triangles in the midfield. Pogba has the best range of passing in the whole squad, so make the long diagonal and other options available to him to make up for his mistakes at the back. But when we come down to brass tacks, in most cases, this means that the most crucial player on the pitch must either find a new role or be dropped.
It's not a matter of being defensive. It's a matter of still having no balance in our game. And only good balance can bring consistency. If we want to move away from Fred/McT, we should not replace either one with a fancy ball-playing midfielder. The rest 8 outfield players, especially the 4 ahead of them, have to work much more on the pitch. I still remember when people were calling Lampard crazy for deploying Jorginho in front of the defence. But Jorginho's play-making from deep is world-class. Did Tuchel sign a workhorse to fix the midfield? No, he changed the set-up to provide protection to the Italian and he also coached Chelsea's defensive transition so that their lines don't look like unravelling knitwear when they are getting back to shape.
This is what Solskjaer needs to prioritize because this is where he's failing tactically.