Hope this boat is good for you!
Power steering, salesman is full of it. If anything a B3 would be easier to steer due to the counter rotating props.
Low fluid won't have any affect until it gets low enough to aerate the fluid - a couple of ounces won't do that.
Could be a few things, stiff mechanical cable from the helm, low pressure from the pump, bad "cylinder assembly-power steering" (that's Mercs official term for the rack on the transom) or maybe the swivel pins on the gimbal ring are too tight.
In the pic you posted of the engine compartment, I don't see the steering cable - maybe due to camera angle? - but a miss routed cable could cause your symptoms.
Power assisted steering vs power steering, that's seems to be splitting hairs. They are basically the same thing on a MerCruiser. Either way it should be buttery smooth. Probably want a good tech to diagnose. If you want some ideas on troubleshooting just ask and I will help, but under warranty - probably best to leave it to the dealer.
Had a wild one a few years ago. Same symptom as yours, ended up that the power steering cooler had froze just enough to crush the steering fluid passage but not enough to cause it to leak water. One of the few times I needed a power steering test gauge to diagnose stiff P/S.
I would suggest getting Mercs pump, this system doesn't take much air pressure, no reason to damage it over $26.49. Plus the pump looks cool in it's special holder!
I've been asked about disconnecting the MerCathode system because the boat will be lift stored. Yes you can, but there is really no reason to. This system uses almost no power when it's out of the water. So no upside, just possible downsides.
Have you hooked up your Techmate to pull the hours?