I have been using the same slot/same downward motion for my nanite injector since I first started playing. I also use the same downward slightly right motion to select my "main" equipment that I pull out the most often.

I have the motions in muscle memory so far that I can literally "feel" them right now as I'm typing this as if I actually had the controller in my hands. I know the exact motion for each of the four equipment and personally I like the way it is set up. It allows me to rapidly transition from one equipment to another without even having to pull up the circle (a quick press of R2 and a flick of the right stick in combination works every time.

Personally, I don't like the weapons placement on the circle. Flicking up, left, or right screws with your aim and isn't as easy to do in combination with pressing a button that naturally pulls the controller forwards away from you. Pulling down on the stick pulls the controller towards you, giving you a better balance.

As for the straight line thing, I think you're pressing the control stick before you press the button...cause when you press R2 your aim is disabled while you select an item. Pressing it fast enough results in almost no change in direction. Also, the two main downwards motions for the middle two equipment should at most aim your character downward, which doesn't affect direction at all (another reason why putting the equipment on each 90 degree angle is a bad idea.)

Customization would be nice though. Other control options or something.

My problem is not the placement, but the proximity. I try to switch to the "nanite injector" in your example and because in the heat of the moment I "flick" the stick down so fast that it rebounds and selects the item that is on the far right instead. Also not all DS3 sticks are able to differentiate as well as the next. Yours may be better than mine, but I know that over 50% of the time when I try to swap from one equipment item to the next, it never fails to give me the WRONG ONE.

Calling this an "interface nightmare plaguing the game" is getting a bit dramatic...

Even on my Min logi suit with 4 equipment I've gotten pretty used to hitting the exact spot for each equipment. Just takes getting used to. Having said that in the heat of battle sometimes I do switch to the wrong one, which can be frustrating.

All in all not a bad idea though, removing weapons from the equipment wheel would definitely free up some space. Not to mention that weapons in the equipment wheel are completely unnecessary anyways.

Why are you selecting the injector anyways? Select your rep tool and use "o" to revive the player, you can usually grab them for repping while they are still coming up off the ground.

As for the wheel, I don't have a problem with it either. I've had the same tools in the same slots since, well.... forever. 1st slot changes, 2nd is injector, 3rd is rep tool, 4th (if applicable) is nanite. I'd say I'm 95-98% accurate on selecting which tool I want.