Don't be so sure.
We didn't have Gyökeres for the first 3 years, and while we didn't score as many goals as we did last season, we were still decent in attack.
When we had Tiago Tomás or Paulinho playing in that position, our style was a bit different, our offensive 3 switched around, they also pressed more.
Basically, don't look at Gyökeres as the type of player Amorim wants to be his striker. He won't have a problem making adjustments if different players give him what he wants.
He adressed that on his last press conference.
His name doesn't have an accent.
It started when he was playing in Qatar, and he didn't really want to correct them at that time. It kind of stuck since then.
Our reality is different. Despite being a pretty big club, Sporting still has to sell players in order to grow and keep a positive cash-flow. Amorim knew that, which is why one of his focuses was precisely to develop young players, especially academy players, to sell them.
And while United won't have to worry about that, I suspect Amorim will still look at the academy as a way to improve the club identity, but also to bolster his squad without having to buy tons of players per position.
I don't expect him to go on the market for anything other than starting players.