It's still probably the best, simple metric for assessing a team's quality at a glance. At the end of the day it shows you how well a team creates goal scoring opportunities and how it prevents goal conceding opportunities, everything else is down to shot stopping and finishing (in theory).
I think it'd be mostly fair to say it shows who 'plays the best football', less whether a team is actually effective at playing football.
Absolutely, though aren't assist quality and defensive positioning both factors that influence xG and xGA? That's kind of my thinking when saying why it's a good metric.