1. Selling warranties - the better the product the less there is a need for a warranty.
2. Selling support - the better the product, the less there is a need for support.
3. Licensing exception - not sure what that is.
Again, open source today is :
1) Competitive strategy used by big companies against rival - for example kubernetes and its eco-system as a strategy of google against AWS.
2) Bait and switch - also known as open core. For example redis or hashicorp. I will open source a "community" edition to increase adaptation, but all the useful features are behind a wall. I think it was mongo CEO who actually stated that in an interview.
I agree "open source" is mostly a corporate bait-and-switch which is why I focus more on the "free as in free speech" aspect.
However, if my pay is based on support, I have an internal conflict.
There is something to be said about code review (which was the original Linus argument). However, I should not expect quality reviews from non paid developers.