I would’ve had zero issues using cap space this year to do it.
They are playing cap games to bank space as is, so you would need to drop someone on the roster to keep a third goalie full-time and bank cap space for a deadline move. Can't go below 12 forwards and 6 D, so I guess the argument is give up on banking cap space and use Fast's LTIR on a third goalie.
By the time we knew Fast was out for the season and LTIR eligible, all of the good goaltenders were signed. You could pick someone up off waivers, but are they any better than Martin? Probably not. Best argument would be James Reimer, but he signed in Buffalo and then was picked up off waivers by Anaheim when Buffalo tried to sneak him through waivers. So even if he would be of interest, Carolina wouldn't have had priority to get him.
The goalie market wasn't deep. I think Driedger would be an improvement over Martin, but Driedger went back to Florida because he had success there. Going elsewhere probably would have required getting a backup job, not a #3 in the press box. I think Waddell saw the market wasn't deep and that's why he signed Martin back in March to be the #3 this year.
Would you trust calling up Akira Schmid more? Jack Campbell, who is now in player assistance? Kaapo Kahkonen, who was waived by the Jets and claimed by Colorado? These are better known names, but I don't think they are any guarantee to be better than Martin.
I honestly don't feel any better about most of those guys than I do Martin. Like I said, I can see an argument for Driedger but I think I'm biased by his first hot run in Florida before he got hurt in Seattle. He's a complete unknown at the NHL level the past 2 years (2 games in the NHL since May of 2022.)