>I’m curious for feedback here from other designers. My instinct at this moment is to cut diagonal movement.
You're never going to make a game that instinctively "clicks" with 100% of players. I recommend resisting the impulse to fix what isn't broken to reach a broader audience. Besides, you spelled out a much better solution already: Simply rework the tutorial so that moving diagonally is unavoidable and have players repeat it once or twice so it sinks in.
+ Addendum:
I'm reminded of Invisible Inc, which is a fantastic game and works in all the right ways... and has a god-awful tutorial that fails to teach you some of the most important mechanics, such as the distinction between noticed and seen enemy vision. I regularly watch new players hamstring themselves by playing on self-imposed hard mode, navigating enemies under the assumption that the "You get seen and *overwatched* here" vision cone is twice its actual size.
It speaks to the flaws in the tutorial, which not only fails to explain the difference, but doesn't even let you move through peripheral/noticed vision, let alone force you to do so to teach you that it's basically safe. I wish the devs had improved the tutorial, but I am very very glad they didn't decide to instead cut the peripheral/seen distinction just because it was confusing to some players. *Shudder*
