Just seeing this. I have zero issues, steers easily both ways even at high speeds. And I recently added a set of 3 way valves and a steering cylinder onto my kicker, so along with the autopilot pump I've got a more complex hydraulic system than most.
Since it turns both ways smoothly at displacement speeds, problems with the cylinder seals are unlikely.
At low speeds do you get any noise from the hydraulic pump when you're turning the wheel, at either helm? If so, the system still has air in it and needs to be bled patiently and completely - this is critical. It should be whisper smooth, with zero gurgles or other sounds. It should also steer using one finger at idle - if not a fitting or hose is undersized.
Things I can think of (could be a combination of these):
My first bet is the torque-fin on the engine needs to be set correctly to your prop. Even switching hands of props does nothing to convince me the fin is set correctly.
engine set too low, so that anti-ventilation plate is buried in the water, making steering, trimming, etc. difficult at speed because you're fighting the whole plate. This doesn't explain why it is hard one way and not the other but could be a contributing factor and is crazy common. Every boat I work on has to have the engine raised, often 2-3 holes or more.
If all the fittings, hoses, torque-fin pass close, careful inspection, you can start to suspect a malfunctioning helm or steering cylinder. I assume it's the same with either helm?
Curious problem, will be interested to learn what the solution is! Good luck!
