It does no such thing. The suspension load has to act somewhere. Torsion bars are just springs, they put the load on the anchors. Coil over suspensions are no different, they put that load on the lower control arms and the upper spring anchor. Does that really make a coilover set up a better design? It adds the weight of the spring into your unsprung weight (bad), and puts all the suspension forces on the lca. Not to mention taking a car that was designed around having a torsion bar suspension, and then relocating all of those forces onto areas of the frame that weren't intended to carry them.
As far as it being the stiffer springs, no, they're not entirely to blame. I run 1.12" torsion bars on my Challenger, which is a bigger, heavier car, with the same design for the torsion bar anchor. That's a 270 lb/in torsion bar, which is over 2.5 times the original spring rate. No issues with the torsion bar anchors after over 20k miles, and my car DOES have rust.
What you had there was a crappy weld, and it would have failed with the original torsion bars too. Maybe not quite as quickly, but it would have failed.