In the spirit of this thread, I broke a scrap axe handle from House. The mounting end of the haft was already ruined, so this was not a sacrifice.
The haft has good grain orientation, reasonably tight grain structure and a moisture content between 9 and 10 percent.
I wouldnt say it broke clean, but it did break in two with a single blow from that hammer end of a splitter.
As for the OPs hanging, the kerf went too deep, all the way to the bottom of the head and maybe a bit past. You can see a crack forming at the end of the kerf, a sign that the kerf was too deep. The metal wedge was driven in perpendicular to the main wooden wedge, and it cracked the haft on both sides. So its not just a matter of quartering the mounting tongues at the end of the haft, but they were serious cracks not kerfs that also caused problems.
Hammering and leveraging a splitter like that would put a lot of stress on the haft just below the head where it was seriously weakened in four directions. Add in the problems of a widely spaced growth rings, and you have multiple problems all focusing on a single point of weakness