This is an uninformed take. Yes the RSU is backloaded. But during the first two years, you get a large monthly cash sign up bonuses so that assuming the stock stays flat, over the four years, your total comp stays flat. If the stock increases your comp goes up.

I spoke to someone who is there now and when you get your yearly review, now you can choose between mostly cash vs mostly stock for your raise and most people choose mostly cash.

I make the same now as I did when I was at AWS and I much prefer my all cash comp over my less cash + RSUs when I was there.