You're right. Harrison is a better hitter now and the defense doesn't suffer much when Harrison plays third. Then Romy at 2nd may not be as good of a fielder but may be a better hitter than Harrison.
The offense is noticeably better while the defense isn't notably worse.
Since the All Star game Harrison's line is .281, .331, .363, .695
Moncada's line is .172, .276, .276, .552
Seems to me that since Yoan has had some luck in late inning situations driving in runs , he would be best suited to pinch hitting and defensive replacement. I hope once he's off the IL that they don't make the mistake of starting him any more.