I bought a few trees on P-18 in the last couple years. The last was a Sundance from Cummins. Hoping to see what you describe with P-18.I have one coming this spring on P.18 rootstock. P.18 supposed to be a full-size tree, but bears earlier than Antonovka. We’ll see.
I don’t have high hopes for a quick bearing P.18. Fruiting quicker than Antonovka sets a pretty low bar. I planted a Chestnut crab on P.18 in 2019, so that may give me an idea on what to expect. I’ve planted 7 others since then (5 varieties).