A crew neck top can absolutely work for skiing—it's the simplest, most affordable option, and it layers cleanly under mid-layers without any zipper bulk. If you're skiing mostly in mild conditions or you run warm, a crew neck keeps things uncomplicated.
The tradeoff is ventilation and neck coverage. Without a zip, you can't dump heat on a steep climb or crack open the collar on a warm spring day. Crew necks also leave a gap at the throat where cold air can sneak in, especially on windy lift rides.
The fix is simple: pair a crew neck with a neck gaiter or balaclava to seal that gap. If you always wear one anyway, you won't miss the zip. But if you prefer minimal accessories or ski in variable conditions where you'd want adjustable venting, a half-zip mock neck is worth the upgrade.