The worrying thing is how often he behaves like this and seems to get away with it.
A bit of heat on letsrun then next week he's got another brand deal or elite athlete to work with. Are brands not concerned about this kind of thing? Is a few thousand views on a YouTube video worth more?
Maybe it will be different this time as the recipients of his abuse have shared it publicly (although he's also been quite happy to share it publicly himself - IE Strava)
Whilst the abuse is particularly shocking this time, in general it's just par for the course.
Anyone who calls him out finds themself on the receiving end of abuse and threats of this sort of 'ive got X amount of followers I'm going to tell them Y'
Now even if Y is just completely fabricated most people decide to just back off and distance themselves rather than get into a public spat with someone who just has no moral compass at all.
I think that is understandable on their behalf as it's stressful - I guess that's why he does it! but it does give the impression that many of his earlier transgressions (a few of which were summarised above), are somewhat minor. But behind the scenes, they also involve these personal attacks.