I am surprised to hear that Amazon is that low (rules them out as a target for me) - but your comp in terms of salary + stock is not competitive with FB/Google, so comparing to them on vacation time is not meaningful either IMO. In my experience, plenty of smaller companies are more flexible on vacation time over 20 days, so those would be the ones you're competing with.

However, if things are working out well for you as an employer with your current pay + benefits stack, you probably grok the market better than I do. Wish you all the best!