Both cup-and-cone bearings and cartridge bearing can be sealed or unsealed. Sealed bearing is a meaningless way of indicating a specific bearing type. Shimano and Campagnolo uses cup-and-cone bearings (also called angular contact or ACB) bearings and the rest use deep groove cartridge bearings. The latter are a very poor choice for bicycle use but they do have the advantage that if you totally ignore maintenance, the bearing never damages the wheel whereas in Shimano wheels, a rusted cup means you dump the wheel. Campagnolo has a patent for replaceable cups and cones. But as I say, both can be made sealed or unsealed.
Servicing and adjusting cup-and-cone bearings requires some skill, but so does replacing cartridge bearings.
Mavic's nylon bush on the freewheel cannot be replaced from a Mavic spare part. Mavic only sells complete freewheels. Further, the bush runs on the hub's nose and wears that down in time, requiring a new wheel. It is a rubbish system from an engineering point of view. It is easy to service though.