Rotors "Casting Problem"

We own a Dodge Caravan. We have had it for some time now and until recently our brakes have been fine. We noticed some pulsating when applying our brakes and took them in to have them checked. We were told we would need new pads and the rotors needed to be machined. We were fine with that.

When we picked up the van the mechanic told us that the rotors were "not true flat due to casting". He mentioned that there was some pulsating still but it should be better than before. WAS HE WRONG! The brakes feel like there is a large rock attached to the rotors now and we have a THUMP THUMP THUMP rather than a whoosh whoosh whoosh. It is horrible and much worst now.

Is it possible to have a casting problem in the first place? If it is, is it possible to go from a soft pulse to a hard jerking after the rotors were machined or turned? Or is this some claim that a mechanic makes for a someone who has no knowledge?

Thanks for any guidance you may provide.