"You might as well make a deal with the people stealing your content because they are going to keep stealing it anyway" is not a great option.
Part of licensing is the implicit understanding that if the parties do not come to a deal, they cannot use the licensed content. It seems from this article that Perplexity is not operating in good faith, ignoring robots.txt, using unpublished IP addresses, and then lying about the amount of referral traffic generated.
Not to mention, whether or not its legal (and im not a lawyer) doesn't seem to be the issue. It's being so shortsighted that you build a business that steals a product from an unwitting third party, and when that third party is drained of resources, where will you pull from?