Has he really? They have the exact same save % and every Chicago game I have watched, Fleury is standing on his head doing the best he can to keep the Hawks in the game.
Lehner has been doing exactly that all year. People think because Vegas has been a good defensive team in years past that they still are. That couldn't be further from the truth. It's mostly due to injuries, but they've been awful this year.
Moneypuck has Vegas dead last in high danger shots against at 221. Chicago 6th best at 151. Lehner is 14th in Goals Saved Above Expected. Fleury 109th ahead of only Lankinen and Grubauer. Chicago has the 3rd best Expected Goals Against, Vegas 18th.
I'm not sure you can find a single defensive metric for this year that says Chicago is a better defensive team than Vegas. And that certainly tracks with the eye test, having watched every Vegas game.