There are several things in the terms that ATC uses that kind of grate on me. For example, an aircraft might say, "Jeffco Tower, Boeing 4408N to land." This particular Boeing is a Stearman, and in the real world it is usually just called Stearman, even by ATC, rather than Boeing. There are several other aircraft done the same way, though few are as glaring (to me).
Also, in this particular call, "to land" isn't something I've ever heard used in quite this way (or used myself, for that matter). It would seem preferable for that call to read: "Jeffco Tower, Stearman 4408N, with Mike, landing." Or, even just "Jeffco Tower, Stearman 4408N, with Mike," as ATC in the real world generally assumes you are landing if you don't say otherwise.
While I can't recall them off the top of my head, there are a number of other stilted phrases used on occasion by ATC.
While on the subject of ATC, traffic calls are way too numerous (especially with AI traffic set at 100%), often to the point of obscuring other communications, and making it impossible to get a word in edgewise.
And ATC sectors are a bit too rigid, often resulting in a call to change frequency, then almost immediately changing back to the original frequency (or to still another freq).
Of course, as others have noted, there is no attempt made in FS ATC at actual separation of traffic, which can be a hazard landing at a busy airport. This is exacerbated by the AI aircraft unrealistically slowing very rapidly to taxi speed, consequently taking "forever" to get to the next taxiway to turn off. This often results in otherwise unnecessary go-arounds called by ATC.
I recognize that there'd be a lot of development work to change all these, often needing a complete rewrite from scratch of the mechanisms involved, but these are goals that should be worked toward.