You can explain all of that by positing an historical martyr since there have certainly been other such idealistic martyrs in history. Or you can explain it by positing a syncretic myth (Judaism plus mystery religions/salvation cults plus Cynical, antisocial philosophy), created mainly by the author of Mark, a myth that was later historicized largely for political purposes.

The question at issue is whether we can know today that either of those two scenarios is significantly more probably than the other. The evidence at hand may be just too ambiguous for us to know how Christianity originated.