Peak isn't the most points you scored. Tobias" regression is the past 2 seasons, when we really needed him as a stable 3rd option
Tobias scored 20 points as a #1 option in LA, but had pretty decent 2 first seasons in Philadephia, while he had to share the ball with Embiid, Simmons, Butler, Harden (for some part), ...
But scoring 20 points per game as a number 1 option should have warned us a bit. Ingram scored around 23-25 points per game (and also has done it more than once), and on decent efficiëncy. He also had 1 very good play-off run as a #1 option.
It shows that he at least has the potential do be relied on in the play-offs. Tobias has never shown that in his career.
Ingram had a down season and was bad in the play-offs, but the fact he's an ending contract and still only 26 (and also has shown there's more in him) should be enough to validate the risk imo.
He also adds things the Sixers can use (length from 2-4 position), playmaking, iso-scoring, ...
His decline in 3-point shooting worries me a bit, but you can't have it all probably. Otherwise, you will have to pay more.