The concern with Elliott is having to play multiple games in a row. He can spell a starter which is one of the primary purposes of a backup netminder, to play once on back-to-back nights, but he can't be depended to be the replacement starting goalie for a long stretch. That also needs to be considered this off-season. Mediocre defense will make an average goalie look inferior but an average goalie will make himself look worse when he is exposed too often.
It's not even back to backs, it's having to play more than a couple games with only a day off.
At this point in his career Elliott is Neuvirth a few years ago, fine if you spot him, but if you ask more than 25-30 games in an 82 game season you're in trouble. Now put those 25 starts (22 of 49 games so far) in a condensed schedule like this season and you have a terrible goalie.
But if Hart was the Hart of the bubble, he'd have started almost all games other than back to backs - he routinely played 60+ games in junior.
So in that case Elliott plays 15-20 of 56 and is a decent backup.
And ironically, Hart's bubble performance made it impossible to sign a good backup, because what good backup wants to play 20 games, get exposed in the ED and not have the track record for his next contract.