Taken out of context yet again.
He is talking about OGL and that third party vendors should not do that. He immediately follows that up with people can do whatever they want at their own home games.
Nice spin though.
Ok.
1. The fact the subject comes up as part of an OGL discussion does not make it 'out of context'. It merely shows that, in terms of the game as designed (and all the 1000s of hours of thought, play testing and so on that that involved), the designer felt it necessary to state that in his (rather considered) opinion, removing the Concentration restriction would be A Bad Thing, and therefore any officially licensed products would need to adhere to the Concentration ruling, because it is such a serious part of the game balance mechanics for 5e. Which demonstrates his opinion.
2. He does indeed acknowledge that people will probably do what they like at their own tables. I suggest you do so, as this rule clearly bothers you. You may prefer to try and convince those of differing opinions that they are misguided and follow your lead on this matter, but you won't manage to do so (a) with everyone or (b) by belittling them.
3. It's not "spin". A person I don't know on the internet asked where a quote from Mearls about concentration could be found. I thought I'd be interested in reading it, too. So, I took a couple of minutes to find one, and as the person had asked so nicely, I put the link here. My comment that it was a "pretty firm view" is descriptive of the statement Mearls made - he clearly has a firm view on the subject.
4. As it goes, I do like the game as written, thanks, yes. One or two tiny niggles, but I like it. I'm more than happy with whatever value judgements this may prompt others to make about me.
5. Regards your earlier comment regarding Concentration not being affected by states such as Paralysed etc - I think it's common sense to include them as 'other environmental factors' which call for a check to be made. Maybe even an auto-fail for some, if not all, of them.