I'm not sure why some very good NHL goaltenders re-signing on long term deals makes Gibson's contract have any sort of value.
Gibson hasn't had a good season since 18-19 season and basically the only goaltender he's clearly looked better then in the last 5 years is Miller who was 40 years old and toast at the NHL level. Gibson has basically been a replacement level (if not worse) goaltender for 5 seasons now.
I get being optimistic but there is nothing that suggests Gibson is going to turn it around anytime soon, especially as Dostal will likely be the starter for this season. Gibson is a prime buyout candidate before the start of next season.
Gibson has played well in long stretches, particularly at the beginning of the season. Then he wears down due to being pummeled with a massive quantity of shots (a record number) and the constant losing. Comparing Gibson to his backup is apples/oranges. The backup plays less and gets worse matchups (Dostal last year being the arguable exception).
For much of the last 5 years, the ducks have been the worst puck possession and defensive team in the league. I think there is a reason to think Gibson can regain his form and be an above average (not elite) goalie if he plays with better players in games that matter.
And that is where the recent signings become relevant. Ullmark is a pretty good comp to the better version of Gibson. Ullmark just got a substantially bigger (and a bit longer) contract than Gibson. Again if Gibson returns to form (a big if), then his shorter contract with less AAV has some decent value. The larger point - Goalie salaries are increasing which makes Gibson's number more palatable relatively speaking.
And again, If Gibson doesn't return to form, then he has no value.