So, I am legitimately curious: how do wizards express skill in this type of game?
The thing about this question is that it accidentally exposes the entire problem with these "old-school systems = amazing depth" arguments. Because you're right to ask how a Wizard expresses skill in a game like MnM and the the uncomfortable answer is the same as it was for EQ: they really don't. And not because players lack skill (although those that do lack skill often gravitate toward "lazy" classes like Wizard - same as EQ), but because the systems themselves don't allow for it.
In a combat model built around long casts, low APM, predictable rotations, and minimal reactive tools, the ceiling for individual expression is microscopic. In EQ-style design, two wizards of roughly equal gear and level are going to perform within 5% of each other simply because there's nothing in the kit that lets skill differentiate them. And in 2025, people are just going to Autohotkey or AutoIt their "rotations" in a game like this, where combat is so predictable that you can run your script while watching Netflix.
There's no weaving, no animation cancels, no positional optimization, no resource manipulation, minimal-no proc fishing, minimal-no reactive mechanics, no priority systems, no burst windows - nothing that separates a "good" Wizard who's attentive and at his keyboard from a warm body mashing his script every cooldown. The "skill" in these systems is basically: Don't over-aggro. Don't go OOM. And don't fall asleep. And somehow this gets mythologized as "high-skill old school gameplay."
The problem is the system. These combat engines were built in 1999 when "press nuke, sit, wait, repeat" was considered cutting-edge. There's simply no room for mastery when the mechanics themselves are shallow. A skilled player can't express anything in a system that never asks them to. That's why this whole nostalgia push is so weird. People keep pretending these mechanics were deep when they were really just primitive.
Right now, asking "how does a wizard show skill?" is basically asking "how does someone show mastery at microwaving a Hot Pocket?" There's only so much you can do with a one-button oven.