I agree that Landy probably could have gotten more as a UFA, but I struggle to call the rest of them "discounts".
Makar signed his current deal in 2021, coming off his ELC after playing 101 regular season games and 35 playoff games. A - Comparing his 2nd contract to UFA contracts signed by Jones and Nurse isn't apples to apples. B - it was 2021, so he had no hardware yet and was negotiating mostly based on potential. Yes, he has outplayed it and there was always a good chance he could, but from a contract negotiation standpoint, it seemed pretty fair at the time.
Lehk and Nuke both signed in 2022. Despite scoring the Cup winning goal, Lehk had a career high of 38 points to that point of his career, and was mostly a 3rd liner. Nuke had just finished his first career season with more than 35 points. Again, they've both outplayed those contracts, but I'm not seeing much of a discount at the time they were signed.
And Rantanen didn't have a case to be paid as much as Marner. In 2019, Marner was coming off a 94 point season where he was 11th in scoring, 4th in assists, got Selke votes, and led the team in scoring, playing mostly with Tavares and Hyman. Rantanen played with MacKinnon and Landeskog, didn't lead the team in scoring, and wasn't top 5 in any category, nor was he getting Selke votes.