It was the 20th biggest deal ever at the time, and among all active players in 2016 the deal gave Heyward the 18th highest AAV in baseball. It was a big deal but not sure i'd call it a megadeal.
He was also coming off his age 25 season, so it makes sense they were willing to go 8 years. Would they give a 400m or 450m deal to Tucker going into his age 29 season when the extension takes effect, which would make it the 4rd highest contract in baseball history? Very doubtful.
Unless we get good AAV value like the Swanson and Heyward deals were at the time, it looks like the only way we get a player of his caliber is via draft or trade.