IMO, the difficulty of two sports are very similar... in that they both require correct
and consistent mechanics to be even somewhat successful. Both sports require instruction and practice to develop the mechanics of the swing in golf and the stroke in pool... and quite a bit of practice to develop muscle memory for the (correct) mechanics.
As an individual, if we are
somewhat adept at hand-eye coordination there is no reason why we could not become some proficient at either sport.
I've achieved a fair amount of proficiency in pool after playing on and off for the past 45 years (especially in last two or three)... yet until last weekend, had not played a round of golf in my life. In preparation for last weekend, I went to the driving range
once with a golfing buddy and he explained the basics to me... and I did fairly well on the range.
Some of that carried over to the course itself... and I didn't embarass myself too much. ... as I shot ~130 in both rounds on a pretty difficult course (according to my buddy... who was coaching me a bit along the way).
Bottomline... I believe that golf is harder than pool simply because the mechanics of the swing are more complex than the stroke in pool. When you hit a perfect shot in golf you've really done something noteworthy. Making a beautiful shot in pool in pool is definitely fun... but from a mechanics point of view, a perfect shot in golf in a sight to behold as the ball sails down the fairway... or into the cup from 60 feet out. I was fortunate to make a couple of
very good shots last weekend... shots that I'll never forget since they were so beautiful. BTW, the best hole that I shot out of two rounds is I bogied a par-3... I was a happy camper!
At the same proficiency level, stringing together good shot after good shot in golf is probably every bit as difficult, if not more, than doing the same in pool.