I'm not mellored, but I believe the answers would be:
1) 5e-10 - because you stop at level 10 and have plenty of higher level (CR 10+) monsters to spice things up. Complaints about curb-stomping higher level encounters seem to proliferate
2) 5e-10 - meaning you reach the endgame faster (many campaigns never reach mid to high teens, let alone 20th level), I don't think you actually level faster, you're just more likely to reach your full potential (and cool abilities)
3) 5e-10 - You actually reach and use "your stuff" and you can play a lot more at the highest level and still have plenty of adventures and encounters to face without things getting too wahoo.
4) I've often felt that 5e felt "stretched out" to meet the artificial 20 level limit, with most high level features, barring high level spells and maybe some capstone features, being perfectly cromulent for mid-level play. Sure you could just double the advancement rate and theoretically accomplish something similar, but you would still have encounter building difficulty and other high level play problems. This gives you a little bit of the 'E6' feel that was somewhat popular in 3e and keeps things a little more playable and grounded for some preferences.