I went on BRef to try and find similar freshman seasons for guards to what Murray did this season.
18-20 pts per game, 50%+ on twos, 38%+ on threes, fewer than 3 assists per game.
The names that came up were Kevin Martin, CJ McCollum, Tyler Hall (this year), and Steph Curry.
Obviously that's a pretty good range of outcomes. At the very least you can say he had a really excellent freshman season. Those other guys played at much less heralded schools than Murray.
I dunno. Murray passes the eye test for me as a pure scorer. My worry with him is what I've heard from draft analysts on podcasts etc about his ability to turn the corner in the pick and roll, defend off the ball, get to the rim, and create for others. He'll need to do all of those things to become more than a sixth man or one-way scoring starter (e.g. McCollum and Martin).
I would much, much, much rather take Murray than Hield. What Murray did as a freshman at Kentucky is far more impressive and exceptional from a historical perspective than what Hield did as a senior.