I own a Nacra with the fork and I used to run with a Hobie16 with the fork as well.

The compressive load load doesn't affect the mast when the hook is located near the top, it only affect the part between the pulley and the fork.

I had to replace or swage the Halyard wire a couple of time over the years. In order to gave the Halyard go trought the pulley on the mast head, you need to have a large diameter pulley (like an older Hobie16) or to use flexible 7x19 wire and smaller pulley. The flexible halyard will wear quickly and break over the pulley and even the pulley sheaves might break.

The bigger pulley is also more expensive and heavier.

The ring might be more difficult to operate but it has the advantages of being lighter, cheaper and longer lasting.

The other advantage is that the downhaul force is applied directly to the sail and doesn't affect other parts of the mast like the mast head or the the halyard.