That may be true. Personally the interesting comparison w/ Chelsea is Ziyech considering the style and mercurial overlap. He proved far more than AG when he moved, is probably a better player still currently despite having struggled to establish himself in the prem.
But I also think its important to note that even if Gordon kicks on and doubles this evaluation, the funds he could generate considering the timeline it might take to establish himself at that value, might make the deal still worth it to Everton right now. Advocating for this deal is not predicated in doubting Gordon's quality as much as it is a calculation on the offer itself in relation to his current value, and the funds he would generate being more valuable to us then he is in isolation.
I like Gordon, but considering the lack of sell on potentials to generate funds currently on the squad, the opinion that we can reinvest with similar quality over multiple positions from this return (and that being ultimately necessary), the risk that his value could decrease based on the Chelsea offer which IMO is inflated, all point to me the sale being wise at this number and for our predicament.
The clubs circumstance is far more informative than Gordon himself is to believing this would be good business.