No big deal. Each new generation of car almost always outperforms the one it replaces . . . that's just technical progress.
Look at the Porsche 911. Every generation has been "better" than the one that came before it, at least on paper (acceleration, braking, time around the Ring, etc.)
That's not to say that some models don't stand out because of their looks or a unique combination of factors that add up to "soul." For example, there are plenty of people that would choose a mint 993 over a brand new 991, or a 1973 911S over a 1980 SC.
I like to think our 1M has that element of "soul" that will keep it desirable for years to come. Personally, I don't think many people will feel that way about the m135i.
"This is a brilliant, brilliant, brilliant car. And that's all really I've got to say. The end."
Clarkson on the 1M