While I totally agree that goalies are voodoo, I'll also point out that starting goaltenders still get paid a decent rate in the NHL.
Jarry's 3.5M cap hit has him tied for 26th highest in the NHL. Considering there are 32 teams in the League, that puts him squarely towards the bottom of the League in pay for a starting goaltender.
7 goalies currently have a cap hit of 6M or more, with another two at 5.9 and 5.8.
You get down to 13th highest cap hit to get down to a 5M cap hit.
When you look at actual salaries, and not just the cap hits, there are 10 goalies making at least 6M this year.
Considering Jarry's actual salary this year is 4.5M, there's no way he's getting anything less than a 5M cap hit on his next deal. If he continues to perform the way he has so far, a 6M cap hit really isn't out of the question for him.
Regardless of whether you think he deserves that or not, realistically speaking, he's very likely to get something in that range.