The debate is whether countersteering is something you have to consciously do by turning the steering column ("yaw"), or whether it's an automatic effect of pushing/leaning down on the side you want to turn toward ("roll").

"countersteering isn't real" because "steering isn't real", cycles at speed turn by leaning/rolling, not steering/yawing.

Countersteering and roll are not mutually exclusive. The countersteer generally happens when steering whether you think about it or not. If you know about countersteering, you can practice it to make emergency turns.

For roll, Leaning in the direction of the bike is actually a bad habit (but it'll be fine on most road turns)

It turns out you want to lean the bike, and lean/shift your body in the opposite direction. This keeps center of mass above the wheels.

For example, the pro motorcycle racers with their knee an inch off the ground,they're leaning their body weight away from the turn, away from the ground. Meanwhile their bikes are leaning crazy hard.

That style of leaning is important for fast descents, or switchbacks, particularly switchbacks. Eg: "MOUNTAIN BIKE TIPS: CORNERING WITH CONFIDENCE" (start at 1:45) https://youtu.be/GFKPtEzE4xw

If you need to quickly swerve out of the way of an obstacle you push hard on the handle and you will immediately initiate a turn (you could just as easily say that your are initiating a lean). It's also well understood that handle bar input allows you to increase / adjust the lean mid-corner. I ride and never knew there was a debate about this.