When someone argues it would be a huge escalation for the US, UK and France to directly defend Ukrainian territory against Russia's attacks, they should explain how the same nations directly defending Israeli territory from Iran's attacks is constructively and strategically different.
The other would almost certainly end up being called WW3, and would likely involve at least a limited nuclear exchange.
The reason it was “de-escalatory”: It helped Iran prove what it sought to prove: no AD in the world will stop their missiles from getting through. For Israel it provided the face-saving “99.9%”.
Also, the Ukraine situation has no Jordan, Iraq, accessible ocean (ask the Turks about that) to operate from.