No other example is in a closed shop (yet, IndyCar might soon be).
I am not a fan of family-hiring family regardless. Cindric at Penske, Dillon at Childress, Gibbs at Gibbs, Custer at Stewart-Haas and NASCAR is a semi-closed series these days, which makes it worse.
What I was hinting at, was the questions that was left unanswered. How often does it happen that a driver continuously loses to a teammate, but it is the teammate that doesn't get a new contract/are fired?
I suppose technically at the moment neither is F1. Obviously, that is a whole another discussion that is happening now. Nepotism can have positive and negative outcomes...I think it is a case by case basis, given that generally speaking it is fair to say that 2nd/3rd generation drivers have an advantage to opportunity...helps getting the foot in the door. Not a bad thing, just a fact of life and nature of the business...as is having cash. Nevertheless, I understand your feelings about family hires.
As it relates to your question, it seems it has been asked before and answered before. Even I took a basic stab at answering it in this thread or Aston thread. In very simple terms, it comes down to whether people think Massa, Vettel and Alonso are washed up or not. If a person thinks they are washed up, then the case for Stroll being fired is strengthened as he can not beat old guys. If they are not washed up, then the case for Stroll is strengthen by saying what do you expect from an average F1 driver against world champions and almost world champions.
If we really want to tackle that question, I am all for it. However, it does not change the fact Aston Martin is little more than a family owned and operated team with one of the drivers being related to the owner. Does not mean he is immune to losing the seat at some point, but he will be afforded every opportunity to make good on whatever talent anyone thinks he has. He is very experienced and only 25.
I posted on here in several threads that I thought he was destined for management very soon and that he will not make it beyond 2025. His recent statements would seem to indicate otherwise. Could be all PR that he is driving for the long term as reports indicate that Honda might have some influence. We will see.