the real genius of MM6-8 IMO is two other features:
* the ability to stay in real time, which allows you to simply run past encounters that are too powerful, or blow through random low-level stuff. Imagine how much less enjoyable MM would be if you couldn't zoom around somewhere like Darkmoor without dropping into turn-based and being forced to fight every. Single. Thing. on the map. The first time you encounter it, regardless of level. And even running away took 10 minutes because you have to wait for both your party and every. Other. Single. Thing. within range to also move. Only to the extent of your single-turn move allowance, per turn. Seriously painful
* once you kill things, they are gone until the map resets, between 6 months and 2 years from now. The REAL annoyance of Wiz8 is that apart from certain unique monsters, the random monsters out in the wild keep reseting, even while you're still on the same map - as well as scaling to your current level if you happened to clear the area of lower-level monsters at an earlier level
This is how MM6-8 can fill maps with hordes of monsters, which you can simply run past, fly past, or come back to later and blow through with a single high-level AoE spell that you didn't have the first 5 times. This gives you much more flexibility and enjoyability compared to the Wiz8 system.
But I also enjoy the Wiz8 system more than MM6-8 in other ways. The magic and skill system is brilliant, for example. The choices for race and class give you great replayability, even if some of them could be argued to be simply less-optimised versions of the same thing, or have unique abilities that quickly lose value after the first few levels. And the Bard and Gadgeteer classes are fun and cleverly implemented, even if the Gadgeteer is essentially a passenger until around level 10 because, although you keep finding things you can combine into gadgets, you don't find the other "half" of most things until relatively late.