Like some people have said, you need to get used to the little everyday "street" driving techniques to optimize its potential and use it efficiently. Yes it has its quirks and differences with manual, but to master it, you must learn around it so you can have a much more appreciated driving experience.
1. I'm usually in S4 mode myself. Like others have stated, a straight 7 to 2 shift is unnecessary. You have two options in this scenario. If you're lazy/occupied, do not down shift at all and the computer will do it for you as rpms allow. There might be a bit of a jerk depending on which S mode you're in. Second and more recommended option is to multi downshift while slowing down and right before the turn. For example, 7th at 50mph- start braking and immediately double tap for 5th, then maybe single tap for 4th, and just before turn double again for 2nd. Now the important thing is to prepare for the turn in advance, and the combination of double or single taps is at your discretion for the desired gear for the turn. All this will be more and more evident as you experience more driving.
2. Now in D mode, the go pedal is key here in toting the line between aggressiveness and efficiency, regardless of what level you're in. The sensitivity of the throttle input seems to be the difference between the different D modes. Slight pressure of throttle will determine quicker or slower gear changes(if at all) between D1-5. I rarely use D mode but if I do, I almost always use D3 because I feel the first 2 are useless and if I'm in D in the first place, I just want to cruise and not hold lower gears anyway. But if I feel the need to punch it a bit, it reacts quick enough for passing, etc. with a slightly more "heavy" press of the pedal. Again the throttle input/sensitivity is the main factor, and the adjustments could very well give you a close compromise of fast and efficient, but why not just use S mode for that? BTW, any D mode should always go into 7th. Just ease up on the throttle a bit and modulate accordingly.