Maguire is 93rd percentile, mid 70's success rate. But yeah, being average in the air isn't a deal breaker, it's just something to keep in mind. Ramos and Chiellini are/were both great defenders without being dominant in aerial duels everywhere. Hard to quantify that stat in terms of key moments, but its still very useful.
Sample size issues? How? Its the past year and breaking it up into per 90 stats and comparing it with every player in that position in the main 5 leagues and major European competition? Or you can break it up into any season since 17/18 (but that only compares and ranks players based on their own league, not all 5 leagues).
Also no problem! It just came out last week I think, but its great. Shows so much info. I find it's a lot more useful for on the ball/attacking/dribbling effectiveness/creativity information though. Stuff like ball progression, getting it into the box, xA/xG etc. It's good with pure shot stopping too, as you can look up the post shot xG as a difference of how many goals a goalkeeper actually conceded and see how much above or below expected they are.
Defensive stats are much harder to quantify due to the differences in styles, so much of it wouldn't be captured. Not all about tackles/clearances/aerial success rate.