"Buddha was not a divinity nor prophet," So not a religion.

"yet some temples are proud to exhibit his body parts" So do some Churches and Cathedrals (Holy Relics in various Countries) which doesn't make them a religion.

"So involving etymology is of doubtful value as an argument" That is the ONLY way. A religion is something fulfilling the definition of religion... And Buddhism isn't, no more than Janseism, Sufism, or atheism.