IQ is not a reasonable metric for human intelligence.
The matter of fact is that it is a metric of human intelligence and of all known metrics of human intelligence it is one of the best. Considering you still gauge people on intelligence with something you came up internally that you consider reasonable, and that whatever is that that you use internally is almost certainly worse than IQ, I'd say you're full of shit and/or lack logic :)
It is a reasonable measure of intelligent-adjacent things, such as how good you are at taking tests. An IQ score does correlate pretty well with how well you'll do in college. But to say that it's measuring "intelligence" in any sort of strong way is misleading.
There are two questions:
Is it a measure? Undoubtedly.
Is it reasonable? Well, how'd you define reasonable? Would you say that if A is reasonable for something, and B is better than A for the same thing, then from "A is reasonable" follows "B is reasonable"? I would. So if you can claim a person to be a fool and another person to be smart based on some interaction and consider both statements to be reasonable, and if you concede that IQ would better (on average) predict that kind of stuff than you, therefore you should consider IQ a reasonable metric of intelligence. (But you don't, so I suspect you're not good at logical reasoning)
Perhaps I'm not, but at least I'm good enough at it to be able to have a discussion without resorting to insulting the person I'm talking with.
G-factor as a concept exists but can only be approximated by standard tests or equivalent.
IQ tests are imperfect and flawed, but it's the closest approximation to G factor we have.
