the simplest one to look at is Net Rating. Cooley's a +6, and that's playing a legit #1C role. That number has continued to tick up since the preseason projection of +2.
Slaf is the only other one from the draft class that isn't a negative, so that's good, but he's a league average +0, which is down from his preseason projection of +3. Hutson for comparison is at +5. The only two habs ahead of Cooley are Suzuki +11 and Caufield +8, but Cooley's +6 ranks higher among centers than Caufield's +8 ranks among wingers. Suzuki and Caufield are pretty much bang on pace with their preseason projections of +10 and +9.
Cooley's on the verge of being a legit quality #1C already, but not quite there. The bottom end of the C rankings:
+8: #29-31 Hintz/O'Reilly/Strome
+7: #32-37 Trocheck/Nelson/Karlsson/Hertl/Jenner/Celebrini
+6: #38-42 Cooley/Zacha/Staal/Danault/Byfield/
though I think Cooley has been bouncing back and forth between +7 and +6 lately.