If it was done with fiber tape, that is the main issue, paper tape and compound should do it, plaster would be stronger.
If not my solution would be to remove the tape and filler, re-tape with first coat of auto body filler, which needs to be below sheet rock surface; I use body filler as it is stronger then compound or plaster for tough issues like this. Fiber tape *****
Part of the reason people have a dislike for fiberglass tape is because they dont know how to use it, and apply it incorrectly.
Contrary to popular belief, when you apply self sticking fiberglass tape to a crack, and then mud over it, The mud, while it will get squeezed through the holes, generally wont connect to the other holes, so instead of having mud on all sides of the tape, you have mud on 3 sides, and on the 4th side - the important side, you typically end up with 4 billion dimples.
Which ofcourse makes the repair fail.
Instead, mud first, THEN set the fiberglass tape into the mud, then trowel it out and let it set before applying more mud.
Also, plaster, lime and plaster of paris, has a tendency to NOT stick to drywall. Actually, plaster doesnt even like to stick to itself.
However, as bar as bondo vs plaster with hardness, not sure which goes harder, but I do know, depending on your gauge, you can make for an extremely hard plaster finish.
So dont forget to follow these steps when fixing drywall cracks:
1) take a utility knife, and V out the crack, use a duster to clean up the V.
2) mix up durabond 45/90 to the consistancy of cake mix? maybe a little thicker.... and fill the V, and the surface 1" on either side... then lay your mesh tape.
3) let it set... Play on GJ... for an hour.
4) coat it with easy sand, or the goop in the grey bucket with the blue lid, 2-3 coats, and feather it out so its nice and flat.... playing on GJ and drooling over all the pictures between coats.
5) sand smooth, prime, paint.
6) take a picture and put on GJ.
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