I'm not sure what a modern one-handed backhand is. If you look at players like Lendl, Edberg, Becker, and Stich vs younger players like Ljubicic, Haas, Almagro, Federer, Warinka etc. they're all doing the same fundamentals things. In fact many modern players like Haas, Federer and Wawrinka hit their backhands with an eastern grip similar to Becker or Lendl.
Don't worry about terminology like forearm deviation. Ignore 95 percent of the internet forum terminology. It will probably be confusing and do more harm than good. You might be surprised how many high level players ignore terminology like that and focus on the simple things. Most if not all. I guarantee you Nicolas Almagro isn't wasting his time with a thesaurus looking up deviation or supination, and stressing over minutia. Like all good players, he started by learning the fundamentals.
Get set up and coil early. You want your front shoulder under your chin. For topspin, get under the ball. Depending on what type of shot your hitting you will vary how far under the ball you get. You want to drive through the ball by extending your front arm and reaching out in front when you follow through. This is where the power and control come from. Resist the temptation to finish your stroke to early. If you come across too early without extending fully through your contact zone, you will have a lot of difficulty controlling the shot, especially against more experienced harder hitting players. You want to finish your follow through high and way out in front of you, with a lot of space between your body and racket hand.
Prepare early, load up and coil, get under the ball, hit through the ball extending towards your target. It really is that simple.
Look at how Wawrinka transfers his weight from his back foot to his front foot as he follows through. During the side view, look how far he follows through in front of himself. He reaches out towards his target. He has a compact backswing and a long follow through. That is where the consistency and control come from.
Lendl Backhand: Almost the exact same form as Wawrinka. Compact backswing, long follow through. Notice how both Peter Lungren, Stan's coach in the video, and Lendl emphasize early preparation and weight transfer.
Here's Fed and Ljubicic trading groundies. Not many people hit a cleaner backhand than ljubicic. Look how how clean, sound, simple, and repeatable his technique is. That backhand is timeless. At about 40 seconds in Ljubicic hits 2 clean, sound topspin backhands. Again at around 1:07 he hits another good one.
Note: It's not like a forehand, where you are significantly rotating your upper body in order to get into your contact zone and make contact. A lot of people on this forum will tell you that on a "modern" one-handed backhand you rotate like a forehand or 2 handed backhand. This is not true. The people giving this advice are probably internet denizens who do not hit sound one-handed backhands. Ignore their advice like the plague if you want to hit a sound one-handed backhand that is consistent, repeatable and will not break down in pressure situations against stronger players. When you make contact on your one-handed backhand, you will still be turned sideways to the net and your contact point will be early and out in front. As you finish your stroke, your body will uncoil and open up somewhat after you have already hit through your contact zone.
Professional players like Stan Wawrinka generate a lot of racket head speed. As they are decelerating the racket at the end of their stroke and recovering they do open up more. It's important to realize what happens before that point of the stroke.