Managers have some sort of set team that they plan to use, Smalling wasn't first choice in any of the season, he played his way into the team as his performance was better than other CBs. He had similar challenge again (IMO that was wrong move, Smalling should have been our first choice CB). Also there is nothing set in stone. Every position is up for grabs. Don't think Greenwood or James thought they would be first choice players at various times this season, everyone thought (even player himself) James would be squad player but for more than half a season he was first choice player. Then post restart Greenwood became first choice as his performance means he was easy choice.
Matic started as back up for McTominay - Pogba midfield and it looked like he will be leaving, but when he played well he became first choice midfielder alongside Pogba.
Now that Smalling has left and bailly, Tuanzebe, Jones are very injury prone, we don't have anyone who can challenge for CB spots. If Smalling stayed, he could have easily forced his way into first 11.
Anyways can't hold against him, after all the shit got from fans, it was his time to enjoy some other league.
I am not in total disagreement with you here. I actually see that my point is not exactly far from yours. Just that Ole's plan is not good for the exemption he received for his mess up.
Pep had to use Yaya Toure in later part of his first season, despite the whole world knows how the two ain't getting along. Yaya was still there in the first place due to no taker, not that Pep would try to provoke him to perform. In the end Yaya was kicked out. Similarly the Eto'o situation in Pep first season at Barcelona. The point being: the plan is set in stone (these players would get the boot when they have any takers). Manager have to a job to do, so they wouldn't just ignore an useful player to the point their jobs security affected.
In Smalling case, this summer initially was EURO time. Smalling was told the plan for him is that he would be way down the pecking order, not just behind Maguire. See Smalling question for Ole. That's too many CBs we have, Lindelof, Tuanzebe, Jones, Bailly, even Rojo before he was sent out on loan. By the sound bite of the plan, it's about ability on ball, which Smalling is among the worst.
When there is a plan, it's not gonna change by few occasions very soon. It took so much shit show from Pereira, Lingard, Mata in central position, and both Pogba & McTominay long injuries for Matic to be reestablished as a starter; and finally got Bruno Fernandes deal over the finishing line. Ole can be one hell of stubborn person, too.
Now look at our CB situation, even now the plan for ball playing CB is still intact given statistically our defense is not terrible, even though it's not very good when it comes to highest standard (passing well to isolate opposition attack, or dominate forward with quality in certain aspect). I don't see any change to the plan for Smalling, had he stayed. He may play a little more than what was discussed between him and Ole, such as being introduced to contain Giroud this past game, but ultimately, when the dust settle down, Smalling would still be down the pecking order, as the odd one out. Not the same situation compare to how Mourinho adapt to his opposition strength to set up the defense; or LVG barebone squad policy where there ain't as much competition.
Now back to Ole. He wants the CBs that can pass better, but there is no blueprint for a fluid system (yet to be seen) that justifying to tell someone like Smalling, that his playing time would be limited, not based on merit of performance. This team is still relying on the midfield to mainly supply the forwards, and our best weapon is still counter attack. It's confusing to say the least.