To be fair, so did Georgiev. And he's also shown he's capable of being a good goalie and has a history of being better than he currently is. Just two years ago, he led the NHL in wins, put up a .918 SV% and even got a GM to vote for him for the Vezina (probably MacFarland, but still...). But, he's been pretty inconsistent for the last year+ and pretty bad for the first 5 games this season, so his history and capabilities don't really matter at this point.
And that's true for Gibson, too. Over the last 5 years, he's definitely played some really good games, but there have been more games that were below average or worse. That inconsistency is what opened the door for Dostal to take the starting job. And that inconsistency is also what makes him such a big risk with that contract. Teams have to gamble that he figures it out again and plays more average or better games for the next ~3 seasons for him to be worth $3.2m per year. Or, they can roll the dice on a couple of $1m lottery tickets from the waiver wire every year with no commitment until they find someone that can consistently perform at a good enough level.