3. I've been to Tahoe a few times (never mammoth)....am I remiss in leaving off kirkwood and Squaw?? Probably...though, for absolute ease of access to serious terrain the three I've listed stand pretty tall...even next to tahoe's finest. It's not a better than worse than, it's just who delivers the most serious steeps with the least work.
I've never been to whistler, big sky or big mountain or kicking horse either...I get the sense they all would ranks as well.....
Don't worry. No one is going to rely on your list as the be all and end all.
Remember that extreme terrain--what the OP was asking about, if you fall you get hurt at the very least, or mandatory air or straightline--isn't on the map. Squaw has a comprehensive unofficial guidebook, although some of the best stuff off KT was deliberately left out. WB has a guidebook with some lines that it rates triple black, but I'm sure there's an enormous amount of stuff right off the lifts that isn't included. Most places you have to go with someone who knows, or see tracks in an area where you can reasonably scope out the line before committing. If the OP was asking about something easier, that's a different story. And then there's the North Face of the Aiguille du Midi--from the descriptions and looking at it from the tram I'm willing to be it has the most extreme lift served terrain in the world.