2 Gap Zone
Scheme Fits: Run Stopper DE, Run Stopper and Nose Tackle DT, Run Stopper and Pass Rush OLB, Run Stopper ILB, Zone Coverage DB
3 Man Front Spread
Scheme Fits: Nose Tackle DT, Pass Rush OLB, Coverage ILB, Zone Coverage DB
Above are the only two 3-4 formations being proposed, even if 1 of these werechanged to Man coverage, 3-4 teams would have even less flexibility on their scheme and the same can be said for the 4-3 schemes (+ the single hybrid scheme).
No defensive coordinator has decided the entire scheme based on what coverage the DBs are better at playing. In my personal experience, it's been quite to opposite but I realise that may not be true for everyone so that statement is neither here nor there but defensive backs are mostly capable of playing both man and zone when required. A db with a zone preference will fair much better being asked to play man coverage than a nose tackle would being asked to rush the passer or a pass rushing OLB being asked to constantly set the edge and play the run. This is even backed up by the sims logic as looking at the stats of my db's, whilst they are zone corners, they are only 10 points lower in man coverage whereas my nose tackle is 20 points lower in pass rush than run stopping.
I completely agree that the archtypes of front 7 players is going to play a large part in determining the scheme, not just because of skill sets but because of the genetic makeup of each player. You never see teams asking pass rushing OLB's to cover athletic tight ends (unless you are Joe Barry and believe Preston Smith is really a 265lb cornerback) but a zone coverage cornerback isn't suddenly going to forget how to play cornerback because he was asked to play man coverage.
I get the sim won't be as complex as real life and have the ability to run both man and zone because it largely requires the coach to be able to see what is happening on the field in real time but my point is, if we can only choose to play the whole game in either man or zone then we shouldn't have to match our dbs up to an entire scheme. If we wanted to give a malus/bouns for man/zone then I would argue that we'd be better off applying these to the opponents offensive scheme aka a team running a west coast offense could be countered by running zone coverage to stop short routes such as slants/crossers. Give the coach to ability to determine whether they want to 'outscheme' their opponent by trying to take advantage of a weakness in the offensive scheme or rely on the raw ability of their defensive backs to just straight up beat the offense.