My opinion is that view is very simplistic and unnecessarily offensive to a whole class of researchers. MuZero, developed by David Silver, uses a combination of RL, supervised learning, and unsupervised learning (state representation) coupled with a planning algorithm. It accomplished things far beyond anything unsupervised learning can ever accomplish.
Unsupervised learning is exactly the wrong way to approach chess or other games that MuZero solves. It's also worth noting that traditional alpha-beta pruning + heuristics are basically neck and neck with the very best of neural network based techniques. I'll trust stockfish over a alpha-zero or MuZero for awhile longer if I'm trying to win a computer chess competition ...
Sure, Stockfish just uses millions of years of evolution to build its heuristics and can't be transferred to any other game. The point remains, calling RL a cherry on the cake compared to unsupervised learning when they are completely orthogonal and not mutually exclusive techniques is simplistic and unnecessarily offensive.
So it's bad to be the cake? I assume he means it's the foundation one falls back on when the more specialized categories of methods are not applicable.
You might not like my analogy either. I think of supervised and unsupervised learning as the majority of the genome of ML, while RL is that little Y chromosome sometimes tacked on to address a few high-profile tasks.
