By the numbers, it's above a Deadly challenge for 3 "baseline" 7th-level PCs. A Deadly encounter "could" be lethal for one or more player characters. But these characters have some gear, good ACs, and stats. I will assume the players are pretty competent because they're asking for higher difficulty. If they use good tactics and quick thinking, they will reduce the difficulty of the challenge accordingly.
I'd say therefore it's fine, though I would not backdoor nerf anyone's class features. You can take it down from Deadly to Hard with some terrain favorable to the PCs. I suggest some 15- to 20-feet deep pits or craters which will put them outside the roc's reach. If all PCs are in pits, the roc gives up and seeks out other prey. To make it more of a meaningful decision to take cover in the pits, throw some swarms of poisonous snakes in them.