I am always willing to discuss things, so of course I read your reply!
To go one by one;
It's a personal pet peeve when someone goes "I think this is bad" without going into ANY amount of detail as to why is something bad. In case of GC rarely do I ever see people pointing out their actual mistakes (which in comparision to the highest level of play - are noticable and can be pointed out just fine without mockery). I just know people like him go on vlr.gg, look at the stats and brush everything off outside of stats.
I am also aware he doesn't exclusively talk about GC (as I do not either), as I tend to check out people who I am replying to, but the level of comments doesn't seem to be any more articulate when talking about T1.
You can be constructive regardless of the level of play when talking about them, there's a reason coaches exist and that is their primary job within a team to point out these things so they can work on it more. That's atleast what I think should be a role of the coach. You do realize that being constructive has nothing to do with if they're good or bad? You can give thought-out feedback to any level of play.
The Spotlight tournament DID show something, albeit not a lot. Some players can hang around in these lobbies, while others got heavily bodied. Not all players are good, and also as you said, it's an off-season tournament that doesn't always show much (Pacific tournament was singlehandedly something diff). I also question it just like you do, I watched as many games as I could :)
I see who he replied to, but then again, doesn't change much. Fighting fire with fire does not achieve anything. He did not use any sort of argumentative logic to dismantle it, just went "lol they get beaten by T3". Saying that without anything else holds no value in my eyes, as I can do the same thing and say "lol Dodonut T4 GC player beat T1 players they should be kicked off of the roster".
Regardless, I am not here to change your mind and I respect the fact that even if we disagree or differently see GC and its players, you are willing to discuss it into more detail than most sceptics of the league :)
If you read all of this, thanks for considering.