Correct, this patent clause is not for small startup/companies. It is a strategy of Facebook to create a defensive system against patent trolls. They used react as medium because of its popularity.

VueJS has more votes than Angular. Kind of a surprise O_o

I ain't saying what is in post

Angular not have any virtual DOM kind of thing

If Facebook patents cover React (diffing, componentization, etc), those patents likely cover Preact/Vue/etc

you lose the patent license from us if you sue us for patent infringement. well if you are creating something out of this world using react as one of your tech stack and one day Facebook thought of copying it than you will not able to make any claims for that because of this license.

well preact is using tech/concept like virtual DOM etc which is patent filled by facebook.