I'm at 1200+ miles now. I have also been driving my parent's 2012 F30 328i extensively the last couple of weeks.
I've done some tests of throttle response and while ECO PRO is noticeably less responsive, there is no real measurable difference between D/Drive and DS/Drive Sport. The difference is in responsiveness and programming of the transmission. If you engage DS or Manual mode while in ECO PRO you will still have the [poor] ECO PRO throttle mapping. I still believe the delay folks are experiencing is transmission delay (unless my vehicle is different in some way). It seems that in D/Drive the transmission waits at times (asking, "are you sure") before kicking down into the proper gear. No such issue with DS or full Manual mode.
Our X1 throttle response is equivalent to the F30 328i in COMFORT mode as well as our 128i and E90 335i. It is not as responsive as the F30 Sport/Sport+ modes (even in X1 DS mode). The F30 feels more powerful/sporty over all simply because it is lighter and you feel more of the road with the lower suspension. The X1 is much more comfortable to drive on the highway but nowhere near as sporty on the curves. The F30 is a true sports sedan and much closer in performance to my E90 N54 335i than the X1 28i is. I'm hoping the BMS N20 Stage 1 tune will give me some headroom and power closer to the F30 328i.
The 28i really needs to be in the right gear to get the most out of the engine. When you need responsiveness, I recommend you always switch to DS or Manual mode. Only use ECO PRO for highway driving and D/Drive for relaxed driving around town.