Just my opinion of course, but I really liked the RTI in my GS's. I got really good with them and rarely needed to take my eyes off the road to make my more common selections. With the mouse controller you knew where the end of the screen was because the controller was moved to the farthest end (up, down, left or right) and wouldn't move any more. you totally lose that with the touch pad so you have to continuously follow the curser with your eyes to know where you are on the screen. This is the biggest drawback.
I have had my RC for almost 2 years now and absolutely HATE the touchpad. It is extremely unintuitive. It even makes selections (map screen only) without double tapping or pressing down on the touchpad, just by placing your finger on it when trying to move the curser. It gets so frustrating that I almost punched the screen once (yes, I know "anger management").
BTW, when I use a laptop I almost always plug a mouse into it because it works much better than the touchpad.
Of course Lexus could do what BMW does and have an RTI and touchscreen at the same time. I drive a lot of cars and this current generation of iDrive is by far the best infotainment interface I have used (in my opinion).