He's 15 games into his first professional season, he's 8-4-1, his last few games have been really good, and he's just coming off of his first shutout. He's improved every single year of his career.
Yeah, you don't wait around twiddling your thumbs, but that doesn't explain committing big term and money to a goaltender past when Hart would be ready. Especially when the goaltender you're signing didn't fit your team the last time around, and you traded him away.
Honestly, paying a goaltender big term and money is a stupid idea in general. It's more stupid when they'll be 31. It's even more stupid when they are coming fresh to your team. Goaltending is so much about fit with a team and their style of play, and you're basically rolling the dice.