I played at a high level through high school in SoCal. Had several D1/D2 offers but declined to play in order to focus on academics instead. Plus that was all pre-MLS, so the path to pro wasn't as obvious -- or really desirable. Let's face it too, US soccer in the 80s was pretty abysmal. But I have played pickup/fun in both Spain and Brasil with locals so I've seen the contrast even at that level. Plus family members have played abroad. Outside of that I've read all the popular soccer books you all have and probably clock in the same number of hours watching professional soccer (if it's on TV I will watch it -- couldn't care less which league). Am I an authority? Nope. No more than most folks on these forums.
I disagree with you that playing possession is not a skill. I think it's both a strategy and a skill. Heck there are methodologies that completely focus on the foundations necessary to play possession. A coach can't simply say "hey let's play possession this game". It's just not that easy. The reason we don't teach this in the US is because it's hard and requires parents and players to not care about "win-now". Players make a ton of mistakes initially when learning how to play this way. It's just hard and takes massive amounts of patience.
I think there is a time and a place to play directly, low block, high block, etc. Heck even Man City will step out of their possession comfort zone depending on the opponent. In that scenario it's a conscious decision to do so. Unfortunately, very few youth clubs teach these skills so that players have an arsenal of options in their quiver.
Also, Messi isn't the only "outlier". Pretty sure Kante, Maradona, Xavi, Insigne, etc would like to have a word with you

Also it's well documented that EPL players are bigger/taller than La Liga players. Interestingly enough, La Liga teams have fared far better in the Champions League than EPL teams over the last 20ish years. It's really not close.