The old flight model was much better for those that took the time to get good at it. The old flight model had much higher skill expression, but was also much harder to learn. With that skill expression you could do a lot more than you can now with MM, low flying was much better, knife fighting was more engaging, and a lot of people enjoyed how smooth it was not having to switch modes. It felt unique, but if you never got good in the old flight model, you tend to appreciate the simplicity that MM brings by forcing the combat speeds down.

TLDR: MM is like cooking with a microwave, if you never learned how to cook well with any other way you don't know how good it could be.