Draw a force vector diagram, including the attachment point of the halyard, the sail luff and the running end of the halyard and you will see that the mast compression load is the same with either arrangement.

You wrote that the the mast actually sees 1-1/2 (3/2) times the tension and then wrote 25% less tension. Perhaps a typo and you meant 2/3. Either way, that is incorrect.

And why is there no compression load from the halyard if it is locked? Locked on the mast or on the deck it is still placing a compression load on the mast.