need metal-to-wood glue advice (or other ideas)

[Fumesucker]

8. JB Weld is just an epoxy with some fillers in it, it even sticks pretty well to glass

It rather looks like the problem is your holes have become conical, wider at the outside then the bottom so you are depending on the adhesion of the glue. What you want to do is open the bottom of the hole out so it's wider than the top part, once you fill that up with JB Weld and put the inserts in then more wood will have to tear out or the JB Weld will have to break for the inserts to come out again.

A drill about 1/4 the diameter of the hole put in at an angle several times around the bottom of the hole for maybe a 1/4 inch or so should give the glue something more to grab hold of. Work the glue into the holes thoroughly with a Q tip or something similar.

Make sure you put a piece of tape or something over the bottom of the insert or it may fill up with glue, particularly if you use that gorilla glue that expands, your glue is also likely to spill out unless you put the chair on its side with the holes more or less straight up.

What you really have is a case of poor design in the first place, that's a really high stress area if I understand you correctly, those inserts are being subjected to a rocking action rather than the straight pull they are designed for.