Re your comment here:
yes, transient opcodes are better from the EVM “purity” standpoint. But I haven’t heard of any use for the transient opcodes apart from mutexes. I will add the discussions tag, where we should be chatting.
There are many use cases, which are discussed in the discussion thread of EIP-1153. Here is one of them from Arbitrum. Here is the primary motivation, which is much more than just reentrancy locks. Another use case is communicating information from nested callbacks (we do this in the Uniswap V3 router to return the computed amount in for exact output swaps, which are executed in reverse and involve nested callbacks).
IMO this EIP has no advantages over transient storage.