I have a 2wd
B6100, which is a very similar machine, and I find mine easy to steer, which makes me ask the question: does the 4wd make it harder to steer?
Also, last winter, my first winter with this tractor, I noticed the first very cold day that I couldn't steer it all the way to the left. Come to find out the steering box was full of water, which froze. The dealer I bought it from left it outside all the time, which shouldn't matter, other than I think rain water drained down the post, past a probably faulty input shaft seal, and into the 'box.
I drained it, flushed it, and put in synthetic gear oil. Works perfect ever since.
I don't leave my tractor outside, only very rarely.