I would definitely say it has helped. I feel medicine gets easier to learn with more exposure, and the MMS program largely exposed us to most of the basic sciences you will learn in med school. The 2017/18 curriculum was a little different than the 2018/19 one, but anatomy, physiology and biochem are noticeably easier to study compared to the subjects we either didn't cover (embryology, pharm) or had a very brief overview of (pathology).
I don't know about dental, but the MMS felt like a middle ground between undergrad and medical school in terms of difficulty. The material hasn't felt that much harder to learn, but you are expected to know more of it. That being said, medical school is less stressful for the most part. In the MMS, you have to preform well, and there is an entire year and tuition riding on it. If you don't get in, it feels like a waste, and that unfortunately burned a few of my fellow classmates last year. The uncertainty of getting in is stressful. In medical school, once your in, you statistically are going to be a doctor. Even though it's more work, it's more enjoyable. I think this will vary from person to person though.