That integral box steering system is definitely inadequate for a tractor with big front tires and a loader hanging over the front end end. It was originally designed for 2WD tractors without loaders, and in my opinion, should never have been installed on front wheel assist tractors in the first place. This is why 1985 and later tractors came out with hydrostatic steering on those models, which was a vast improvement. That said, the assist should be "OK" if the tractor is moving and the load in the bucket is moderate.
Without being able to drive it for myself, it would be difficult for me to tell you whether or not your assist was in fact normal for the conditions you describe. If you think it is not good enough, I would start by teeing in a pressure gauge and seeing what your maximum pressure is under operation. As I recall (and I'm going off of memory here), those systems aren't good for much over 1000 PSI. If you develop significantly less than that, then if it were me, I'd isolate the pump and test that directly first. If that checks out OK, then I'm suspecting an internal leak in your box. This can easily be confirmed by monitoring return flow when the wheels are up against lock. There should be little to no oil flow.