Over the past 5 seasons, Aho has the 14th most goals and 23rd most points among NHL players. This, while being on a team that focuses on defense (top 3 defensive team in the NHL over that stretch) and for a player that plays in all situations. He's AVERAGED 38G, 81P per 82 games for the last 5 seasons combined and he rarely has missed much time for injury (Covid shortened seasons are the reason for less games played for 2 of the seasons).
His contract extension, would make him the 17th highest paid player in the NHL today, if his contract were to start today, but it won't. His contract starts next year where a number of other players (Pettersson, Nylander, Dahlin, etc..) may likely get paid more than Aho, pushing him to around 20th.
In an environment where the cap is increasing, his contract is just fine based on his production and performance in all situations at both ends of the ice. I don't think it's a "steal" or "discount", but it's inline with his production and performance especially with the cap rising.