McMillan looks like another Drake London or Michael Pittman to me. Big receiver with a small possession receiver's game. I just don't see the high-octane speed or burst to rip off huge chunk plays.
A shifty 6'5" receiver is still a coverage problem for almost any CB, and London and Pittman have proven that you can be successful with that skillset. Pittman is playing on a fat second contract, and London is about to get one after this season, so in a vacuum, I think McMillan will be a good pro.
But Tet is the kind of guy where, if defenses double CeeDee and leave him one-on-one, he'll body out the corner for a slant or hitch and make an 8 yard catch. If you ran that play with Travis Hunter, he may catch that slant, make a move, and rip off 20 more yards after the catch. Or he runs a fly route against that one-on-coverage and Mosses the corner for a huge gain.
I don't hate McMillan as a player, and I think he's an 80 catch a year guy in the pros. But he's not the kind of alpha-dog X receiver that usually goes top 10 in the draft, and he's being pushed up by a weak class. London went top 10 back in 2022, and if you hindsight-drafted that class today, he wouldn't go top 10 again. He'd go first round (and so would 2021 second-rounder Pittman), but you wouldn't take him over an explosive WR like Garrett Wilson or Chris Olave.