Monero was released with an intentionally crippled hash function. Whether the Monero devs realized it or not, the crippled hash was included to give someone an unfair advantage.
Please quantify this advantage in terms of % of the eventual coin supply of 18.4 million.
Advantage after 20 yrs or so is not relevant to defining a fair launch. Fair launch is used to describe multiple factors during the first few days/week/months of a coins existence.
80% is mined in the first 4 years. Is that a good place to start?
That is a fair basis.
What percentage of the 4-year coin supply was mined before the crippled hash function was fixed? This is very rough but I think the number is about 2%
So yes, the coin is (arguably) 2% unfair. By the standards of the altcoin space that is pure as the driven snow.