I really don't think baseball has as many subtle nuances as cricket. I'm not belittling one sport compared to another, but baseball is a simpler game than cricket. My point is, essentially, that batting in cricket is more complicated than batting in baseball. There are a variety of shots played in cricket depending on the ball bowled and the bowler bowling. Baseball is essentially the same action used by batters (obviously with some nuances that matter and I may not understand and am willing to be corrected on), but in cricket a drive, a cut, a leg glance and a pull shot are all completely different actions biomechanically, plus you are dealing with a bowler who can choose to do a variety of things with the ball and bowl it in a larger zone than baseball pitchers (who might pitch slower or curve balls or whatever, but have to put it in a hitting zone).
Maybe a different way to look at it is if you took a couple of coordinated 20 year olds who'd never played baseball and cricket and asked them to become proficient at batting in both, which would they develop at quicker? I'm guessing baseball because biomechanically it's a much simpler technique with less variance from the bowler/pitcher.
The simplest way I can explain it is to talk about how many 'non-batters' in each sport have some level of success. As cricket fans we've seen countless tailenders, with average techniques, score runs - even against good bowlers. It doesn't happen every time, but it happens frequently enough that there are a whole heap of cliches about having to take all 10 wickets etc. Everyone in cricket bats and, forgetting about the quality of their techniques for a second, everyone (with very few exceptions) is capable of scoring runs. You talk about the nuances of all the different cricket shots, but an average or poor batsman doesn't have to play half those strokes if they don't want to. If they can defend and have one or two scoring shots, they're capable of being at least a nuisance, and possibly much more (see Richardson, Mark). I know that part of the appeal with cricket is the aesthetic side of it but if we're just thinking practically, it doesn't matter how the runs are scored.
With baseball, on the other hand, if you're not one of the absolute top guys you're ****ed. As I said before, even the best hitters only have success a third of the time. In terms of the range of different shots/variations there might be less going on than in cricket, but just getting the basics right is pretty damn hard. I honestly think hitting in baseball is made to look easy because unless you watch a full game, all you see are the important hits and batters having success. Much like with cricket, power sells - so it's all about the home runs. Sit down and watch a game of baseball for three hours and the ball will dominate bat the vast majority of the time.
So, looking at this hypothetical situation with a couple of 20 year olds who've never played either sport, I'd say they'd become proficient at batting in cricket much more quickly. They might not look pretty, and they'd be quite limited I'm sure, but if they could defend their wicket they'd go alright. I really don't think you could expect them to become even somewhat proficient at hitting a decent pitcher, at least not quickly.