Nice work, glad you had the "get me home axles"!
Seeing that it is a passenger side axle... In all of my axle breakages with 26" tire, the overwhelming majority were the passenger side inner right where yours broke. With unequal length axles the tail-shaft housing of the trans is the support for the axle and its somewhat sloppy so if you get any twist in the joint (the joint has play in it by design) I think it puts some slight bending into the shaft to help the end break. The early trans' actually had a bronze bearing there and the later ones just use the aluminum. Its loose because there is oil slosh only to lube it so cant go tight like rod bearings... I think a redesign with an actual roller or ball bearing would help a ton.
The weak link in the passenger side with equal lengths is the half shaft/u-joint, so if you make a custom shaft and eliminate the joint like Shadow did I could see it being much better for durability. I thought for 2 seconds about doing this until I realized the 2.4L block is different so I'd need to fab a bracket bearing, etc that I unfortunately don't have free time for these days
So instead I went back to the smaller tires and let the clutch take the abuse on the launch. I've only broke one axle since on the smaller tire and it was in the DS inner joint and not the spline and I'm guessing that axle had several 26" tire hits on it. I'm interested in seeing the axles that are in it now to see if the splines are straight or not, but I'm guessing they are OK. they will need to come out cuz the clutch probably needs a rebuild now LOL
Before the DSS axles I broke a stock axle end off on a 24.5" tire and only DSS axle spline ends on 26" tires. I actually made just over 200 passes on the first set of DSS axles before one broke (on the 26's). The DSS axles and there are some differences. The stock axles look like case hardened and the DSS are thru hardened and I've tried a couple different heat treatments with them to reduce brittleness. Some that I've broken there were actually in the major diameter just outside the splines. This tells me another issue is we are limited on shaft diameter...
Leaving soft helps. I could never leave soft enough with the 26's but maybe part of that was the twin disk on/off switch. Also, when the axles didn't break the trans definitely took the abuse. I've broken several bearing end plates and two ring/pinions in the past 2 years. .. DJ, hurry up and figure out launch control and T850 dog box
Oh, and If there are enough that want DSS axles, I'm down to organize a group buy shouldn't need too many sets to get a discount.