Firstly, what I mean by positional proficiency is how proficient a player is at playing in a certain position on a pitch (e.g. ST(C), AM(L), etc) not the attribute "positioning".
Some might think this would be an absurd idea, but when I think about it, the current, and long-standing set-up of players' positions really is a nonsensical part of Football Manager that has little reflection on real life.
What does it actually do? People will probably respond along the lines of "it shows how suited a player is to that position". But, what does that actually mean? If you had two players with the exact same details, but the only difference is that one was an ST and the other was just an AML, bearing in mind they have exactly the same attributes, would the AML out-perform the ST if both were used as an AML (in different games, of course)? It's difficult to test this via a holiday simulation as the AI will change positions around if he's not suited to that position.
Now, I don't know whether it has any effect in-game or not, but upon reflection of real life, it shouldn't. Surely the attributes of that player determines how well he does in that position, no? For example, off-the-ball and positioning attributes, alongside decisions, vision, etc.
Then there's the annoying thing in game that most players take ages, if ever, to get to a "natural" proficiency in a position. This is absolutely ridiculous, in my opinion. In real life, if a player has just a three-month spell playing in a position that he's never played before, you know it's going to be one of his natural positions by the next FM. There is also the flip side to this that, every natural position in a player at the start of the game, or when the regen is created, will never ever drop down to accomplished. However, over the years in FM, we've seen players constantly changing their natural positions between different games. So, if the different FMs can change players' positions with such fluency every season, why is this not reflected in a single FM game over the course of several seasons?
Just to use a personal in-game example, I have a Chilean regen, who I bought at 18 as a CM, accomplished at DM and AM, but ineffectual in all other positions. However, based on my tactics and his attributes, I wanted him to play ML instead. So, I've had him training as an ML ever since he joined, and played him there almost every game, and by the end of the first season, he had reached accomplished as an ML, which was pretty decent. However, it's now 3 years later, I've kept him training as an ML the entire time, played him as an ML in 99% of the games he plays, and yet he's still stuck at accomplished? Makes no sense. What makes even less sense is the fact his best season for me was in the first season, where he started off as ineffectual as ML.
It's also pretty stupid that some full backs are ineffectual as a wing back, despite wing back being their preferred role as full back. Same as wide midfielders not being proficient on the wings, and so on.
Sorry, but none of this makes any logical sense to me, and hasn't made any logical sense to me for years.
So here's what I suggest to replace FM's current set-up on players' positions. Instead of the positions being preset by the game, they should be set by the manager of the club. So, at the start of every pre-season, or every time you sign a new player, you tell each player what position you plan to use him the most, and that will be, in effect, their natural position. You can also tell the player what other positions he might occasionally play in, which will in effect be their accomplished position(s). Some players can argue with you, as your preferred AML prefers playing as an ST, but in my opinion, this is realistic. You can also talk to the player during the season to tell him you might want to start using him in another position. You can still play players outside the position you initially stated to him, but do it too often and he might lose trust in you, or angle for a move away to play in his preferred position (for example, Daniel Sturridge was being played as a winger at Chelsea, but was reported at the time that he chose to move to Liverpool to play as a striker). So, there should now be two different position types for each player: the current manager's stated positions for the player, and the players' preferred position.
This wouldn't be a dramatic change, as by and large, most players play in a position they would feel they're suited to anyway. But quite often, especially in modern football, you see a new manager come in, and completely change some of their positions, or sign them to play a completely different position to how they played at their previous club. For example, Milner/Delph were played at LB in the first season Klopp/Pep joined Liverpool/City, despite never having played there before in the vast majority of heir careers. Thierry Henry was a winger when he was at Juventus, but was immediately used as a striker once he joined Arsenal. Valencia/Young converted to full backs at Utd. There are also countless occasions where I hear a player started off as a youth player in a completely different position to what they play now.
The versatility attribute, with the above in mind, should also be scrapped. Milner plays a lot of different positions for Liverpool, but this is because of his all-round qualities, not because of once simplistic attribute called versatility. A generic versatility attribute should also in theory mean he could be a CB, ST or even a GK, but his attributes don't fit these positions, hence why he never plays there, despite his great 'versatility'.