Wood filler is hard, sure. But it doesn't adhere to the wood very well at all. Try this in your spare time. Take two bits of wood, apply wood filler to them, and clamp them together until dry. do the same with another two scraps and use expoxy. Now try to pull them apart. What do you suppose will happen to the parts held together with wood filler? Do you think there will be a noticeale difference between the wood filler and the epoxy?

That's good that you have the first part of your problem fixed. I'm not sure I understand what you mean with the second part though.