It's possible that your scion (Rainier) is outgrowing the rootstock which gives the dwarfing you purchased. But this appears to be a young tree; if I use the grass as a comparison. If it's young make sure there is no tape, for instance, girdling the tree which may kill it. It's also possible that the scion was larger than the rootstock when they were grafted. But if that's what happened I wouldn't know how the graft was done.

It does appear that the graft union is not much above the level of the ground.

The tree is 8 years old, and when I planted it the graft union was several inches above ground level.

Is there bark on the trunk portion below the graft union?

yes, it looks like regular bark.

Scion is growing faster than stock. Otherwise: is there something sticking up over on the left?

No, that's a leaf