You shouldn't blame Arsenal fans if they are expecting so many goals from Gyokeres next season because the hype on Gyokeres is too much, and Arsenal fans are expecting him to live up to their expectations. Arsenal is a club that's good at set pieces, and they always create a lot of chances for their strikers, so I believe if Gyokeres is clinical in his finishing, he can be able to score 20 goals for Arsenal next season.
It's very rare to see a player who played in Portugal league can perform in English league just in one season, I don't remember which player did that. We saw Gimenez perform in Dutch league and when he played in Italian league, he's not able to perform.
Gimenez also scored against Bayern Munich, Lille, and Manchester City when he was in Feyenoord. The same thing how Gyokeres scored against Manchester City, Lille and Leipzig.
I agree the hype is too big, but we should expect lower.