See there's no way this can go anywhere. If I say I don't like it, you guys say I'm closed minded. Nothing to do but agree to disagree.

People are saying you're close minded because you made a sweeping statement that's why, you don't have to like anime but making statements like the one you did says only one thing.

Gee, how dare I have an opinion. How closed minded to not like a thing you've experienced extensively.

See, that's exactly the point I tried to make:

Mushishi: no high school aged characters (well there are childs in some episodes, but the main character is an adult men), no mascots, no too colorful hair

https://www.google.de/search?q=mushishi&hl=de&gbv=1&prmd=ivns&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjv3K7f3cjRAhVDCZoKHUD6DaAQ_AUIBQ

Serial experiments Lain has an high-school-aged heroine, but besides that your analysis is off

https://www.google.de/search?q=serial+experiments+lain&btnG=Suche&hl=de&gbv=1&tbm=isch

Parasyte Maxim has an high-school-aged hero, but involved in all the action are people of different ages. No mascots, no colorful hair and melodrama if you think the mincemeat-murders are melodramatic - well that's your point of view.

https://www.google.de/search?q=parasyte+maxim&btnG=Suche&hl=de&gbv=1&tbm=isch

Nuichijou has no high-school-aged heroes - they are younger. Cutesy mascots is true for that one. Also colorful hair. Yeah, we found the sort of Anime you watched so far. Anime targeted at children.

https://www.google.de/search?q=nichijou&btnG=Suche&hl=de&gbv=1&tbm=isch

Akatsuki no Yona matches also most of your cliches. So two out of five. Still in my opinion very different to Nichijou.

https://www.google.de/search?q=Akatsuki+no+Yona&btnG=Suche&hl=de&gbv=1&tbm=isch

Also a word to the technicolor hair. I met some japanese students here in germany. They tend to color their hair and in some cases in unnatural colors like blue or green. I guess it's somewhat boring if everyone has black hair (as japanese have no blondes, brown-haired or red-haired people naturally, all habve black hair - or white in old age).

Making a sweeping statement is not really giving an opinion, if someone comes out and says 90% of white people are racist based off the behaviour of people like Trump you can expect the same types of responses.

See there's no way this can go anywhere. If I say I don't like it, you guys say I'm closed minded. Nothing to do but agree to disagree.

 Let's look at it from the other side. Did you realize that no Hollywood film has ugly actresses. They just don't cast them. Even if the movie is about an ugly, all they do is plant glasses in her face. Most Hollywood-movies sport heroes aged in their twenties or thirties (equivalent to your high-school-aged animes). Hollywood movies shows action but seldom consequences. If the hero beats up a thug, we don't follow the thug in the hospital where his family comes and is sad. Most women are depicted in one of multiple categories: damsel in distress (still), romantic interest for the hero, overly shallow, as a protagonist often an overly romatic and at the same time clumsy one, or a unrealistic supernatural heroine. Most Hollywood movie have a clear distinction between good and bad people. Bad people drive german cars. You have always something happening. Really. Never once we see the uneventful life of Joe Everyone. And so on.

Would it be fair if I lump all Hollywood together?

Every entertainment product has tropes. That is natural, we live all in a cultural bubble. But we don't see it for our own bubble. We concentrate on the differences. We never say: how should I distinct Jim and Chloe, they both have a head, a body, two arms and two legs. We concentrate on the facial features and can distinct them. If you lump all Anime together you say: they all have a head, a body, two legs and two arms, so they're all the same.