Scott Sinclair was at his peak, had nearly 100 PL appearances behind him and only managed that scoring season once. Edouard has consistently scored goals, at a very young age including at u21 and in Europe.
Don’t look at the league (which I admit is pretty poor), look at the player. He has all the attributes required to be a top player. He will always be a handful for defences and he will score goals. He could easily be a £100m player in a year or two. It is a lot of money but you are paying for raw ability and potential.