four year vest doesn't mean you get all the RSUs at the end of four years. or if it does, that's not how it actually works at google, facebook, microsoft, etc. typically you get an offer with a certain amount of RSUs, and then you get 25% of that each year. amazon is an exception; you get most of the RSUs in the third and fourth year. but you also get a large signing bonus paid over the first two years that mostly makes up for that.

tl;dr: your yearly TC doesn't change much at these companies unless you get an actual raise. I don't fully understand the reasoning behind the four year schedule, but AIUI, it does not strongly incentivize sticking around for the full four years unless you assume significant stock appreciation.