As a reference, I often weigh in the 210lb range, + for bikepacking/bike camping, I carry 30 to 50 pounds on the bike. This puts my riding weight into the weight range of your friend. I have yet to damage or tweek one of my carbon wheels while fully loaded, descending at speed on very severe terrain. (rock fields, sand, root fields.) - I ride on 50s at my loaded weight
I built a set of more traditional wheels. 3X lacing, using 13 or 14 gauge spokes (2.0 or 2.3mm spokes.) on a DT350 or equivalent hubset. For rims, if the frame can fit them, I'd go with a 29er/700C carbon 30mm wide rim, (27mm wide at the narrowest)(rim weight will be in the 400 to 420 gram weight range, with a minimum of 38mm deep.
At his weight, he should be riding tubeless anyways. Using traditional tubed tires, he will get a lot of pinched tubes. (If needed he can add tire inserts.)
Other comments. Since you stated "Gravel wheels" I assume that this would be for an existing 700C based gravel bike. This means he has 142mm wide rear hub and a 100mm front hub. For his weight, I'de be riding a minimum of 40 wide tires. If his frame fits wider tires, I definitely go with 42s, and even better if he can fit tires closer to 50mm.
If he plans on throwing his weight around on corners and doing some real bashing, I'd have him consider ditching a traditional gravel bike completely and migrating to a 29er hardtail 1X12 with a carbon fork and drop bars. Then procure a set of boost carbon rimmed wheels (148mm rear hub and 110 front) he could ride a set of lightweight XC wheels that could really take a beating.)
