Your previous statement—that a user must store the data regardless of node configuration—was factually incorrect and the source of the disagreement.

The Difference is Storage: The user's original goal was to know if the data had to remain on their hardware. The technical answer is No, it does not.

Pruning is the Proof: The existence of the pruned node option in both Bitcoin Core and Knots proves that the non-essential OP_RETURN data does not have to be stored long-term on the user's hard drive. It is deleted after initial validation.

Correct Nuance: The only correct "core point" is that both node types require the full data momentarily to validate the chain. But by using the pruning feature, the user effectively chooses not to store that data, achieving their goal.

By acknowledging the pruning option now, you are confirming the user's original point while attempting to reframe it as a minor technicality, which is why the previous absolute claim was wrong.