Molly and Mikayla will be complementary players whenever they are on the floor for UConn. Whether one is more valuable than the other in that role depends upon a number of factors. I can speak with authority on this subject since my lengthy but undistinguished basketball "career" was spent entirely as a complementary player.
First, defense. A complementary player absolutely has to play good defense. Why? Because there are others who are asked to score. If you are not helping keep the other team from scoring, then, there is really no reason to keep you on the court. Mikayla is a very good defender and her 10 steals in 146 minutes is by far the best ratio on the team. Molly is a good defender but not as disruptive as Mikayla. Neither is expected to get a large number of rebounds but Mikayla is somewhat better in that regard as well. Neither of them foul much.
Second, ball handling/passing/running the offense. If you are not going to score a lot, you at least have to be able to hang onto the ball and to get it to those that will put it in the hoop. Both know the offense. Somewhat surprisingly, Molly only has 6 turnovers this season and her turnover per minute rate is identical to Crystal`s. Mikalyla has 11 and a slightly higher turnover rate per minute. Molly has 10 assists in 96 minutes, Mikayla 9 in 146 minutes. So statistically Molly has a slight edge, although the eye test suggests to me that Mikayla may have the edge. At a minimum, both are adequate.
Finally, shooting/scoring. Again, this is not the primary reason to be out there. I think Geno has confirmed this in his comments, although he has also wistfully wondered out loud who is going to score some points from the bench crew. What is important on the offensive end is keeping the defense honest. You cannot win playing 5 on 4. If your defender is going to cheat off of you and provide help elsewhere, then your presence on the court makes it harder for your teammates to score. At this point, the stats clearly favor Molly as she is 7 for 11 from the field including 4 for 6 from three point range. Unfortunately, Mikalyla has only made three baskets in 146 minutes and is 3 for 17, 0 for 3 from three. Molly has shown herself to be an adequate, if reluctant, shooter with pretty decent mechanics, maybe a slightly slow release. Mikalya`s offensive game, both taking it to the hoop and shooting from the outside, seems to be in a bad place at least for now. Other posters have covered that in detail already. (Note: there are teams where a bench player can come in and provide "instant offense", a la Vinny "microwave" Johnson or, for us older folks, Frank Ramsey. No such luxury here.)
So Molly seems to me to have the edge right now as the first guard off the bench. While Mikalya may be a better defender, the defense at least has to pay some attention to Molly. It is way too early to think about next season as that may depend in large part on the work that they put in during the off season.
As fans, we will continue to root for Molly to become less tentative and to react more and think less; and for Mikayla to stick with it, to not shy away from her offense, and to hopefully see some positive results on the offensive end that will improve her confidence.