From an engineering standpoint, the Rolleifix would need another solid connection to the camera body around the bend on the back of the backplate. Since there is no such support or connection....
I've mounted my Rollei on a ballhead for years without damaging anything, and an Arca-Swiss plate is no different from a screw-in ballhead.
Kindly feel free to correct me if my logic seems ass-backwords.
I won't quibble with your logic or engineering. I'll simply report my limited experience with a Rolleifix: The connection to the camera is very strong and secure. Although it seems flimsy in concept, the part is solid cast metal. And although those little pointers on the front of the main casting might appear to offer little connection, in reality those two points on the front are very solid. The Rolleifix slides into the slot on the bottom plate and pulls itself tight to that plate and to the front points. The three points eliminate side-to-side torque. The solidity of the casting, the way it pulls the back's bottom plate to itself, and the solidity of the two front connections eliminates front-to-back torque.
In other words, it actually does work.
Rollei had an advantage over most manufacturers of TLR: they made hundreds of thousands over years, and they had some of the best machining and engineering traditions and skills the world has ever seen to draw from. Making so many body castings and so many backs and bottom plates, they could afford to spend the time to make something like the Rollefix actually work and expect to earn back that investment. I know, a very alien concept in today's rapid turnover rapid change design world....
Of course none of this negates your experience of using your Rolleiflex without a Rolleifix for years without any problems. I've used a variety of TLRs on tripods over the years without problems, many with backs much weaker than the Rolleiflex. I could see where the Rolleifix would be nice if you don't have the mindset or time to treat the camera right.