You don't _have_ to exercise if you leave. That part is totally optional - in fact, the company will probably be quite happy for you to leave without exercising.
The original complaint was about paying taxes when you are granted options, which is not a thing.
The fact that one would receive significantly less salary compensation vs FAANG has nothing to do with taxes or startups really, it's just plain and bad decision making. If one is going to get a salary cut, one should make a rough analysis valuing the options/stocks adjusted for the few scenarios and compare.
Plus, 95%+ of Engineers (senior or not) don't get into FAANG, so the generalization is not appropriate.
In practice, most people assume the value the equity and options to zero, and always assume it is cherry on top. If you value the stock at zero and get a massive pay cut, then it's just a bad decision.
No need to throw the baby out with the bath water.
