That is one heck of a bike to be riding casually, kind of like driving a lifted Wrangler to the mall.
90% of your trouble sounds like being out of shape. Just keep at it and you'll get better. The other 10% come from the wheels that come on the Haanjo - too knobby, too wide, and probably too low-pressure for efficient road use. You could just try different, thinner, smoother, higher-PSI tires (<35mm, fewer knobs, 60+PSI).
Think about how much you enjoy riding and what your future wants might be (but don't overthink) and let that guide your decision on which bike to get. Will you want to ride longer? Faster?