Okay okay, I just got thrown into this topic and read thtough it... so first of all, please don't use me as a measurement. People are different in achieving things, and not every kart game is similar. Even if I need 10000 hours to... let's say achieve every GOD standard in MK64, it doesn't mean that another person would need as long aswell. People are differently skilled and may have other ways.
Also: earlier MKs are not to be compared with the newer ones. Of course standards may seem weird, unachievable, dumb or whatever you want to call it, but they are meant to be challenging. I am not even close to good enough to judge the MK7 standards, but let me say this: there's many games where every standard has only been achieved waaaaay after release. Just as perfect example, the SMK RR PAL 5lap standard. Even ~25 years after it's games release not every standard has been achieved. It's not because players aren't good enough to get it or the standard is set too high. It's humanly possible, just veeery hard to achieve. And that's what GOD standards are for: it should be a motivation to grind for better times...
Who knows, maybe new strats will be invented over time and those standards will be achieved... how much time he invests into the game, it's all factors that you cannot predict 100%. To be honest yeah, achieving all GODs in MK7 when not even a single person has all standards at GOD is ridiculous, but maybe his motivation will get him very high... sooner or later