You're right in your words, but, in my opinion, to a certain extent only.
Yes, having strong scrim partners is important. But is it all? No, not even close. The difference between the scenes is in the mindset far before being in the scrim partners and what not.
See Gambit Gaming. Have they ever and constantly had scrim partners? Nope. Are they constantly practising? Alex Ich has explained countless times that they don't.
Firstly it's about being good, genuinely good (unlike Doublelift and other deluded NA players) and secondly it's about how you use the practise time and how serious you take it.
Asian teams, and some European ones as well, take it as job. As a career. They take it as serious as they can. It matters not if you scrim a lot, if you're going to do it the pathetic NA way where it's mostly about playing matches with a kicked-back attitude and then spending the following time non-constructively arguing with the team.
The crappy excuses have to cease if they truly want to improve. The same goes for some European teams like EG who think their only issue is "not playing enough solo-queue, not scriming enough and not spending enough time with each other".
Hell, but in the end maybe they don't even want to improve that much. As long as the money keeps flowing and their scene keeps being so little demanding, I bet they'll happily keep focusing on the fame, the drama and the trash talk that the NA scene seems to love so much...