People use S4 worlds and how TSM managed to get out of the easiest group stage in literal LoL worlds history a lot as a benchmark on how NA is stronger than Europe at the moment.
You're right that EU took longer to catch on on getting 'official' coaches and all that noise, but that's simply because there is more money in esports in NA than there is EU. Maybe that set back EU a teeny, tiny bit - I doubt it's by a substantial lot.
If you look at EU LCS as a benchmark, the standings show that there is one clear bad team - MYM and the rest are very competitive - Who'd have known Gambit and h2K would step up as much as they did? I could go on about every team in EU that isn't MYM, but I'm not going to because you get the picture.
Now if we look at NA teams that aren't TSM, CLG, C9 and Impulse. The water gets a bit choppy, you have Liquid and Gravity, the two 'mid-tier' teams, Liquid being a clear cut above Gravity imo, even with all the Piglet nonsense. But then you have the bottom 4 teams, who look like absolute shit. NA LCS did not need the extra 2 LCS slot expansion, especially when you have teams like Coast and T8 who simply just look pathetic. The NA talent pool stops at Team Liquid, Europes talent pool stops at MYM, who are soon to be replaced by xPeke's team most likely.
Now, more relevant teams in one region makes for better scrim environments - something CLG have mentioned is hard for them in NA, and if you look at why - there really isn't many teams that play the game as smooth as they are supposed to. the bottom 6 teams in NA are still figuring out how to make efficient map movements and are still figuring out the S5 meta which is quite franky pathetic, while EU has had the map movement thing down since s4.
Watch both EU LCS and NA LCS and really listen to your own opinions. Reddit being made up of a dominant NA user base will always neuter anybody mentioning that Europe is a stronger region. When the #1 NA teams top two players are both european - you kind of need to ask yourself - Is european talent stronger than american? The answer in pretty much, 90% of the time yes. - Excluding players like Aphro, Sneaky, Double and Meteos. True NA talent is a lot more sparse than you think when you actually break it down.