This point can be made about any of the groups with weapons in this context. Including Israel. So it becomes useless.
Piracy (more precisely: systematically and arbitrarily attacking vessels in the open seas) is not considered legitimate for any government - not the US, not China and certainly not Israel. The violation of this rule by itself is grounds for war by the injured governments (which, by the way include most of the EU and the US).
The extraordinary claim here is exempting the Houthi extreme actions from the rule of not practicing piracy just because they are hostile to Israel.
The above line of thought also begs the question of what other extreme actions are supposedly justifiable if the perpetrator happens to be hostile to Israel. Is it a get-out-of-jail card of some kind?