I don't think you're looking at this the right way. Of course you can argue against it, that's why it's a theory and not empirical game canon. But saying "it could also be this" isn't really how theories work, you have to try to directly disprove it. You haven't really done that, you've just said "there's no reason to think it has to be this" which is missing the point.
I really shouldn't have to but I'll respond to each individual point.
1: Well what I said above kind of negates all the arguments about Pryce (which again, we're really arguments). You've just said it didn't have to specifically be this, but haven't really said why it can't be it. So it's still a valid explanation as any. How out of place the comments are is really irrelevant, I never brought that up. Maybe the video did but it doesn't really matter, the point is Willow is his middle name and that's a fact. Going by a middle name is pretty common. Honestly I find the biggest argument to this is the fact that all professors have the tree as their last name, not their middle name.
2: As for aggression between the teams, there kind of is already. They already have conflicting views on Pokemon, and are at conflict with the gyms, which are not yet standardized and do not have badges and all that yet. It's not something that is hinted at directly in Go, but that's why it's a theory.
3: It would make sense if Kanto was the only region where the war was mentioned, if the war was a civil war that took place only in Kanto. Which would make sense with Go, since it's only Kanto at the moment.
4: Again, that's not saying how there was no way that Pryce was involved in the war, it's just saying "it coulda been something else" which is not really a substantiated argument. There is no reason to say it was one or the other. This is a case of having the conclusion first and the evidence second.
5: Taking place in the real world is an interesting point, to be fair. This is kind of where the lore and the actual gameplay make things difficult.
1/4-I guess what I was saying was that the theory could potentially be true, but I don't see enough evidence in its favor to back it up as being true. A lot of the points of the theory are almost complete speculation (which is what makes it a theory), such as Pryce was professor Willow and fought in the pokemon war, which was between team Mystic, Valor, and Instinct. Since we don't know about Pryce's backstory, I can't actually make any claims against what he was or was not. He could've been Professor Willow, a run of the mill Pokemon trainer, or even a stripper in his youth for all we know. It just seems very unlikely that he was something other than a standard (probably talented) Pokemon trainer before he became a gym leader, but like I said before he could've been anything because we have nothing to work on, so I cannot directly disprove that part of the argument.
2-I know the different teams had differing viewpoints and ideologies, but they didn't seem on the cusp of war, nor even heading in that direction from what I've seen in Pokemon Go. However, that being said, it's plausible that opposing ideas about how Pokemon should be used could drive them to war sometime after the 'events' (I'm not sure what to refer to it as) of Pokemon Go. I never really thought of Kanto as a civil war, mainly because I think there would be some remnants of it somewhere in the form of an old battlefield or graveyard in the games, mostly the graveyard part.
3/5-If we think about Pokemon Go being in the Kanto region rather than the real world because there's only Kanto Pokemon, then the theory is less of a stretch. I'm just not sure if that's how Pokemon Go is suposed to be viewed (form a lore or gameplay standpoint). Also, with subsequent releases of new generations of Pokemon, gen 2 is already confirmed I believe, it will no longer be safe to say the game is exclusively in Kanto.
So really, all in all, the theory can neither be proved nor disproved without some other further information. If we look into the anime, there may be more things to work off of (against the theory), but it's not considered part of the main series games canon so we can't use it, which bring me to the underlying idea the stops me from believing a shred of this theory. In regards to the main series Pokemon games, the anime isn't considered canon, the comics aren't considered canon, spin off games such as mystery dungeon, shuffle, pinaball, ranger, snap, and Colosseum (I believe that some people think differently about a few of these, but that's mostly beside the point) aren't considered canon, so what makes Pokemon Go so special that it would be considered canon in the main series Pokemon games canon?