JB weld would be a very bad idea.
This is a mechanic joint area just like the gears in the transmission. There is movement present they are just straight cut gears. The Moly takes the load off the spline actual metal surface.
The splines will last a long long time in the condition shown from your picture. Clean all the red off and use a Moly paste only. I use TS70 moly.
FYI there is no movement up and down ON the spline joint just the faces hitting each other during rotating use. The bearings inside the splined flange eliminate (most .001"?) up-down movement where most think it might be a lot more, only rotational "slapping" at that location. The bearing races in the flange and all the other bearing races create a long "sleeve" from left to right in a cylindrical layer just out of the axle. So there is no up down movement on the spline flange at the driven flange. When you tighten the axle nut you are locking this sleeve of races from left to right. Everything rides-slides-rolls on that cylinder.
One of the key items to keeping the "crud" or water out of the spline areas is that Oring at the base of the male spline. It seals up against the female spline where the female splines are chamfered when everything is tighten down. If you have the pumpkin off the bike insert the male splines (and push it in) and look down in there, the oring seals the spline joint up at the chamfer.
FYI my splines have 332,500 miles on them and are nearing half worn in width of the spline. Your's will make it 2,500 miles if you use moly paste and a good Oring. I'm going to replace mine soon.
Final comment. Many think it's important that male splines stay with the original drive pumpkin female splines in order to preserve that "wear' condition. If you think about it every time the wheel is removed unless it's returned to the exact same spline to spline location you've changed the wear point on the splines joint on each wheel install.
I've never heard of anyone trying to reinstall the male splines back into the same female spline it was removed from. This is a designed wear joint and compared to the Valkyrie's similar design the ST is a great design! The Vakyrie is missing those all important spline hub 2 small bearings.