Rotor quality is part of the issue. If the mechanic used low cost, off brand rotors, then they probably used low cost off brand pads.
Rotors with thinner cross sections COULD actually be better that those with thick cross sections. Metal casting used to be an art but today it is science. Many factors that affect the quality of a casting include the exact alloy, impurities in the alloy, the height of the riser, and one of the most important is how the casting is cooled. Castings that are cooled progressively following the ideal cooling curve will result in a very dense casting where a poorly cooled casting will be very porous.
A thick porous casting is not as good as a dense thinner casting. But even a good dense casting can be too thin, I’m just saying that thickness is not necessarily the best gauge of quality.
Now pads also are subject to some of the same quality factors. The pads are a composite of a friction material and a resin binder. For any given friction formula, the higher the friction material to resin ratio, the better the pad. But to reduce the resin and increase the friction material requires higher pressures and longer baking times.
The resin in all pads will cook off as the pad is used. Braking generates a lot of heat. The resins will give off residues as it cooks off. More resin means more residues. Some of the residues will stick to the rotors, especially rotors that are more porous. The residues will cause the surface of the rotors to develops differences in the coefficient of friction with the pads that leads some parts that grab more than others. You feel this as a pulsing in the brake pedal or a vibration in the car.
There are a couple of ways to reduce this variation on the surface of the rotor. One is machining like you had done. You can also replace the rotors as many people often do. Myself, I just go out and do a couple of hard 60-5 stops on a lonely road. Go hard on the brakes almost to ABS activation of lockup. Lighten up if either of those occur. Two of those are usually enough to temporarily solve the problem.
I say temporary because as long as you have high resin content in the pads and porous rotors, this will come back no mater what you do. Turns out high quality pads and rotors are cheaper in the long run. Who knew.