I think no. A halyard to the bottom does not double compression. It halves downhaul tension. After all, you do not pull the downhaul to a specified tension - you pull it until you achieve the desired sail shape (i.e. mast bend). If you have a halyard instead of a hook, you reach that shape with half the downhaul force.

That's after taking the slack out of the sail. When sewing a mainsail, one prestretches the bolt rope, and then lets some of it retract into the luff tape before sewing the ends in place. That way, the first couple inches of pull on the downhaul put tension on the fabric along the luff, causing the sail to take the desired shape. You don't, however, want the sailcloth to take too much load (outside its elastic range) and permanently stretch or tear the material. The process above causes the bolt-rope to take up the strain at this point, and more downhaul will induce mast bend. The bolt-rope will have some small stretch, but no so much as to damage the sail.


Now we're entering the realm of dynamic analysis, which is much more complex. However, crew weight, side forces, spreader rake, and tension are the same whether you have a halyard or not, so they don't affect the outcome. What does matter, is rig behavior in a big gust. With no halyard, the sailcloth and boltrope stretch a little, and the mast bends some more under the additional pressure. Hopefully, the extra mast bend is greater than the sail stretch, and causes the sail to flatten and depower (or at least not to power up) in the gust. With a halyard, the sailcloth, boltrope, and halyard all stretch in a puff. The mast also bends, but not as much. You don't get as large or as consistent a depowering tendency. How big this effect is, and how much one sails in big gusts determine whether or not a halyard is a significant consideration.

My boat can be rigged either way (halyard or hook). The vast majority use a hook. It lets us get away with a lighter and stretchier (i.e. cheaper) halyard.

Regards,
Eric