It’s like a professor who did happen to get tenure listening to all the post docs talking about how awful academia is. I’m happy for that one lottery winner but their experience doesn’t count for anything.
Most startups are dynamic, most big corporations are not. They are 'big' because they are sitting on a value chain monopoly.
The same chocolate bars have been in my grocery aisle for 20 years. Variations on the same soap.
Some startups are very poorly run, but most are not led by 'unrestrained jerks'.
If you are going to a startup and doing a very rote, repetitive thing, then you're not very lucky, but most startup jobs are definitely not that.
The risk is that there is 'too much dynamism' and people and up spinning their wheels, over pivoting, crashing. But that's definitely 'dynamic'.