let us not forget that Mike Hearn was also responsible for one of the biggest FUDs that was spread about bitcoin. back in the days (i think it was 2015) that he became butthurt and decided to leave bitcoin, but instead of leaving it behind like a civilized person he decided to spread some FUD about bitcoin first. long story short he said bitcoin is going to die soon. this was when price was about $400 and it had a big dump afterwards down to $300 or $200 if i am not mistaken which is a large drop because of a simple FUD (near half).
Passionate people abound in Bitcoin, to be sure. Hearn certainly did cause an uproar... and he seems to take credit in the AMA for causing Bitcoin to slide in price (20% actually, not 50% as you say, which recovered shortly), but I don't think anyone ragequitting even in those days would have ever killed of Bitcoin.
I suspect the only developer that will ever have an impact on Bitcoin (price) will be Satoshi him/her/them self/ves.
P.S. AMA wasn't half as exciting as I'd have expected. Thought to see some of the old fire return.