Selection effect.
Everyone who thinks "the biggest difference I can make is staying in/joining/founding new AI research lab" does that.
Everyone who thinks "the biggest difference I can make is leaving/whistleblowing", does that.
Treating both groups as the same by virtue of employer is the goomba fallacy.
Some are worried by the AI directly bringing doom; others are worried that one of the companies who control the AI will become a dictator; still more think becoming a dictator is a necessary step to safely prevent anyone else making unsafe AI.
Painting them all under one brush is like dismissing all animal welfare causes in general, because you disagree with specifically Jainists about a policy of non-violence towards all living creatures being relevant to how you reincarnate: the one is way too specific for the general.
What happens when everyone else (who is not so careful) gets to the same threshold three months later? How does them getting there first stop that happening?
It's an utterly self-serving argument and it's not even internally consistent.