Currently I think Cooper is a pure 800 runner that leans slightly towards the 400, though I wouldn’t call him a 400/800 runner. He ran a 4:06 mile back when he was in 1:45 shape, now that he’s in 1:42.5 shape (if I had to guess), he likely can run 3:55 and a 45 second 400, both relatively similar marks.
In the future, assuming he continues to improve, I think he’ll improve at a slightly higher rate in the mile than the 400 since he’s aerobically underdeveloped, so if I had to guess whether he’d be a stronger championship 400 vs 1500 runner, I’d take the 1500. But for right now, he’s just a 800m guy (and will continue being so in the future, but will be good enough to move up or down).