1080p60 recording has very strong compression artifacts, default Neat Video not reducing them much
I assume the actual data rate is 3.3 Mb/s, not MB/s (bits, not bytes). This is very low for 1080p60, and artifacts are likely at such a low rate. You might consider capturing at at least double that rate. 

Alternatively (or also), halving the frame rate to 29.97 would double the effective bit rate. You would be trading some motion artifacting for less visual artifacting, but the former is usually much less noticeable.

Considering that blu-ray can handle in the range of 40-50 Mb/s, your bit rate is way below the target for the delivery medium you've chosen.