Sporting president is making one mistake, which is going back on his word, otherwise asking for a lot of money isn't really wrong at all. If he just came out and said "hey , I want 100 million, that's it" and that was the last of it, then anyone who paid 100 million would get him, that is even more than right now, and nobody could say anything, Gyokeres is a player under contract and the team decides how much they want, end of story.
The issue was, Gyokeres and Arsenal worked out a deal, where Gyokeres and even his agent is making less, just to make sure this deal happens, and Sporting gave a number, which everyone worked towards, but then, Sporting wanted more, and that's the real issue here. If you give a price, you stick to that price, you do not change it higher when that price is matched, that was the bad part of this deal.
I am happy that when the deal that Sporting always tries to complicate, Arsenal do not back down and continue to try to get Gyokeres. So that no matter how difficult the obstacles are now Gyokeres can at least be separated from a club that only cares about money. It is the club's right to set the price of its players especially as the top goal contributor, but it's a different story if Gyokeres has a fate like Oshimen. In this case Gyokeres must thank Arsenal and after officially Arsenal expectations of him are really at stake.