The move makes some sense looking at the market and regulation.
They have to offset the fleet average and to do so you have to downsize your engines and car size, and BMW isn't doing the later.
Another view to look at it, MB is going 4cylinder Turbo with the upcoming A45 AMG (or whatever it's named) & Audi is getting the same hp & tq out of a 5cylinders on the RS3..
With the proper tuning, you can have 300+hp out of a 4 banger. Mitsu & Sub are doing it, depend on where the cars are marketed..
My problem isn't with the powertrain as long as it gets the proper hp and performance to satisfy the M name. My problem is with the stupid look of the F20..