You’re all missing a very important point here. If scripture is to be believed (which is a big if) the highest ranking Roman in Jerusalem, P. Pilot, publicly disagreed with the execution and only begrudgingly went along with it. He apparently even went so far as to visit the site of the execution himself and have a notice mocking Jesus’ enemies nailed above his head.
Allow me to present an alternative scenario:
While Pilot was visiting Jesus he was feeling deeply troubled by it so went aside and had a brief word with the guards asking them not to mutilate the body. So, when the time comes to speed up the deaths instead of breaking his legs they just poke him with a spear. They’re still mindful of Pilots instructions, so don’t push it in deep enough, botching the execution.
Jesus is then taken off the cross to the tomb, where John realised he is still alive. Rather than tell anyone and risk the Romans finding out, he tends to Jesus’ injuries in secret and makes up some story about Jesus rising from the dead to cover his ass from the potential legal ramifications ( this is why his account of events post-crucifixion is so shifty). The story then leads to Jesus’ entire ministry being reinterpreted in light of the “resurrection”. Jesus then dies a few weeks later from his injuries, but there were enough witnesses seeing him alive for the cult to go viral.
Not saying it’s true, just more probable than the official version.