Here's another option from the AAA website. STEEL OARLOCK STAND
You don't need anything under an NRS oar tower to prevent slipping in my opinion. I've run them for more about 10 years without a slip of any kind. I've jammed on them plenty on Sept. MFS trips without any issues. They are definitely not weak. My experience.....others may have different experience.
I don't think I'd call the AAA/DRE oar towers a design flaw. That's just how set screws work. They dig into the rail to hold. Lots of folks use speed rail fitting type frames and are quite happy with them. I used them for one season until NRS came out with the taller 10 inch towers. No movement, no complaints. I prefer the NRS because they are infinitely adjustable, and easy to remove from the frame without taking the whole thing apart. With a DRE speed rail fitting you have to slide them on & off the frame.
I have seen a few boat frames with the rotating rainbow type towers, but I don't know which company they were made by?
The link above is the type of tower my friend has on his older Recretec aluminum frames. They make risers for them, so he can adjust the tower height that way to suit taller rowers who use his boats.