From the blog posts slack has released we know nothing about their security practices.

They have a lot of high quality security features and you can see they actually work because they alerted Max that his account was compromised.

Saying their security practices are extremely poor based on an incident they had in 2015 when their company was 1/20th the size it is today is ridiculous

It's relevant because as a security minded CEO...he did not even enable 2FA on his account.

Regardless of the issue, that still reflects very poorly on him.