Sporting CP is acting this way because they want a bigger profit, especially since Arsenal is so clearly desperate to sign Gyokeres, and they haven't considered any other options for their signings. So, I'm not surprised this transfer will go through; we just have to wait for the official announcement.
Despite Gyokeres's high price tag, I think Arteta knows which players are suited to his coaching style, which is why Arsenal is so keen on Gyokeres in this transfer window.
You know the funny thing with this deal? Sporting are hoping to cash out loads from this, making sure they capitalize on the desperation of the Gunners but forget that the more adamant they are in releasing the striker, the less keen he'd be to continue at the club. Victor Gyokores wants to at Arsenal despite offers from clubs like Man UTD and the rest but the way his club is handling affairs is making it look like they just want to frustrate the player.