“I think that Mashiach has a different status than other ikkarim because the Gemara says that it’s an explicit nevuah of Zecharia and doesn’t provide any way out of that (as a justification for R’ Hillel)”
The Maharal says similarly (Chiddushei Aggados Sanhedrin p. ???):
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???? ?? ???? ??? ?? ???? ??? ????? ????? ?????? ????? ???? ???? ??? ??? ???? ???? ?? ????? ??? ???? ??????