Updated after round of 16:
Dominance ratio:
Djokovic 1.64
Alcaraz 1.50
Medvedev 1.45
Games won:
Djokovic 68%
Medvedev 68%
Alcaraz 64%
Removing Sinner since he lost. Alcaraz has overtaken Medvedev in dominance ratio, if my math is right. Med still has the lead in games won but I blame that mostly on the first round. Daniil had a truly overmatched opponent, even by ordinary first-round-slam-match standards, and Alcaraz's opponent retired before things could get too lopsided. If Koepfer had finished the match at about the same level as the portion he actually played, then Carlitos's games-won % could be a point or two higher and the gap between him and Medovic wouldn't look like a whole lot. Djokovic is still comfortably ahead in dominance ratio.
Surprisingly (to me, at least), Medvedev has been the best on return. Almost half of return points won (49%) – Djokovic and Alcaraz are several comfortably lower (44-45%). On the other hand, he's been the least efficient on serve. Djokovic has been the most efficient on serve and also winning about 1.3% more return points than Alcaraz. Obviously opposition matters in such a small sample size, but I'm not really seeing any obvious outliers in any of these guys' opponents who would radically skew things (the way Sinner's stats would have been against Zverev, say, had he won that match).
Think it's fair to say Novak has still statistically been the best (of these three, I haven't looked at Fritz or anybody else), but the margin is narrowing.