Basically, witness data is only necessary for proving *authorization to spend*. It can be discarded and it is what happens with pre-SegWit clients. The witness merkle root is committed separately of the main merkle root. Inscriptions store data in the witness which can be easily pruned, and also is cheaper (which does not matter, except for the fact that economic incentives will push people to use it). OP_RETURN is committed to by the main block hash. Unlike the witness which can be separately downloaded and if needed ignored from the main block data, the OP_RETURN is part of the main transaction. This means you have to download OP_RETURNs to be able to verify a block and much more important guarantees like: - no double spends - conservation of supply

good chance this is a perfect encapsulation of the entire messy issue