The RSU vesting schedule at Amazon is nonstandard but it's not an issue. You may only vest 5% of your RSUs in your first year, but everyone is given a significant monthly cash bonus to make up for it. The compensation strategy at Amazon is that you always make the same "target compensation" each year, even your first. You aren't shortchanged just because you vest less RSUs in your first year.

An example with numbers: someone in their third year at Amazon makes $150k/yr salary + $150k/yr RSU vests, for $300k/yr total. In comparison, someone in the same position in their first year at Amazon makes $150k/yr salary, but only makes $30k/yr RSU vests, for $180k/yr total. That seems shitty, right? Except the person in their first year also gets a $120k/yr cash bonus, bringing them up to the same $300k/yr.