Many of his "random bullshit go" type gadgets blow up. His actual serious inventions work perfectly. As a child (Clemont is like 10-12 in the series so think when he was like 7-8) he built a city-wide system that can charge Electric Pokemon and it worked amazingly for years on end until TR screwed with it. His robot was specifically made to analyze combat and become more and more skilled. I agree it's not Supercomputer level but it is a highly advanced AI that still nearly fried itself trying to understand Ash.
Still doesnt qualify for Extraordinary Genius but like, as much as Clemont is an intelligent inventor (his age doesnt necessarily matter, it just shows his potential), the anime version at leats made it a huge, consistent gag in itself that his inventions have a lot of flaws and will blow up over the slightest overload. This can speak to Ash against the average trainer, but it creates a huge level of uncertainty given Clemonts track record. Clemont works on a trial and error basis rather than getting things right the first time.
Clemont gets Genius in his general engineering and intellectual prowess, but that obv doesnt translate to his Pokemon battling (hes skilled at it as a gym leader but not to that level. You'd say he was smarter intellectually than someone like Diantha but shes a better Pokemon trainer than him in every way as the champion). Either way, this at its core says that Ash is just extremely unpredictable which doesnt necessarily mean you're super smart. We know Ash is strategic but its not something he thinks about deeply. He thinks of things on the fly and can stick to it. This doesnt translate to his Intelligence and more that he has a slight resistance to Analytical Prediction for example
As for the rest of your points.
1) Gifted works well for beating characters who simply have decades more experience than you, and Ash's ingenuity. You dont need to be a genius to do any of what you described. and its not like Ash cakewalked the Masters 8 (Fell for Cynthia's destiny bond, Leon had him on the ropes and was more disadvantaged in that fight for letting Ash use all 3 of his gimmicks). None of the characters you listed qualify for Genius really either, and the Cynthia Anime profile lists her as Gifted (I wrote that profile tbf but she genuinely hasnt shown Genius capability. Shes intelligent but the series never elaborates by how much). He's never outwardly portrayed as someone thats just in a league of his own either, and works very much on instinct and adaptability.
2) Ash varies a lot more in what region. He's a lot dumber in Unova for example (for whatever reason) than prior regions and he hasn't dont anything completely unfathomable, even someone like Fantina or Paul could copy his unique techniques such as the counter shield just by observation. While there should be separate ratings for his time in other regions, that'd need a whole CRT. Heck, Ash is the sorta character, like Goku and Naruto, that could qualify for multiple timeskip profiles