I am looking for a midlayer. Would this be adequate? I am 6'3" 175#.

I would midlayer this only if you were also wearing one of the crew neck versions (short or long sleeve) as a base layer if temps are going to be cool at all. If you're standing around very static you could get chilled though it would depend on the outerlayer (a softshell or something to block the wind would ramp up the warmth very nicely). On the other side of things, one of the best points of merino is that it regulates heat and sweat so well you don't really overheat in it, so no worries about having too much on.

It depends on the type of activity you're looking to wear it during and the temps at which you wish to do them at. If you're looking to do a vigorous activity in moderate to cold weather then yeah it would work as your mid layer. If you're looking to a low exertion activity in cold weather then it probably would not be warm enough as a midlayer. Their term midweight is not the same as midlayer. Midweight refers to the insulation it will provide. I would definitely view this as a base layer. Not exactly sure what your height/weight has to do with its ability to keep you warm.