I fully agree with that design principle and I think that it will move the game in a healthier direction. The same principle, in theory, should also be used when designing a champion kit: between (A, B, C), pick two. Unfortunately, newer champions basically get (A,B) for free, can do C with some effort and can also do that extra D. Old champions were a lot more "linear", which doesn't necessarily mean that they lacked any depth.
There was a user who compiled a document (and then posted it, here) showing which champion kit was actually overloaded (spoiler: Camille and Ekko are really overloaded). Newer champions, by far, outclassed older ones, except perhaps some reworks which are basically new champions, like Aatrox.
Unfortunately, I highly doubt Riot will follow this direction.