Even then, it doesn't mean the two are 1:1 in terms of size - fully evolved Pokemon got downgraded from High 6-C a few years back largely because of this.
It unironically does, do you know how many calcs and shit we have that rely on Pokemon locales being equivalent to their real world counterpart? Enough for me to say that saying otherwise is extremely, extremely suspect and every other calc that uses the real equivalent for scaling or methodology is going to immediately be called into question. There's cherry picking here, it's all or none unless ample evidence suggests otherwise. And besides, it is the case, if we're not doing that may as well calc everything the way we see it on screen in game, even though that's really not the way to go about it, as I doubt anyone here would say and argue for like 3km Kanto, or something.
Game lake is basically a puddle.
That's entirely due to game limitations, it isn't a unique thing and definitely not an argument unless you think towns are mere feet wide, mountains are like 10-20m, and so on. We know for a fact the games aren't to scale, we're even told the sizes of things at points, that don't correlate to how big they appear, like Mt Chimney being over 500m tall, that one kalos route being a few kilometers, etc. Pokemon games aren't to scale is all, that's why in the games, it's that small.
This lake has no large island in the middle, it would have one if it was one of the lakes.
I mean, it IS one of the lakes, Hareta lives in the forest around it, and we see it again later when Cyrus goes to take Mesprit, no island that time either.
Though unfortunately, you and Gyro might be right, while your arguments for why it shouldn't count is definitely something I don't get behind, I skimmed through the manga in chapters where this locale and lake shows up, and I can confirm, it's small as ****, unfortunately this in turn means the explosion too, and the mountains around it, aren't exactly large either, the explosion is probably more 8-A+, maybe low 7-C based one how large that manga portrays that area in other shots.