The 280ai is a very nice cartridge and I enjoy shooting mine. However, I would not recommend it to a non handloader since the factory ammo options are very limited. He could buy reduced recoil factory ammo for the 300 win and essentially have a 30-06 but that is not as fun as getting a new rifle.

If the goal is to reduce blast and recoil then a 270, 308 or 7-08 would be a step change down from a 300win depending on the weight of the rifle.

If he gets into reloading then 280ai or 6.5-284N would be great options.