Sulphuric acid can damage some plastics but mainly the bendy accordion style or metal pipes.
If it is used in drain cleaners some additives must be used to slow it’s reactivity. Lye, or NaOH, has one disadvantage - it makes scares and then you feel burning. H2SO4 burns and then makes scares.
That’s worrying just because I have a suspicion that there are accordion pipes. So I just did a test. Plugged the drain & filled the sink to the top with water. Pulled the plug and ran to the basement. There is a strong gushing from the main pipe. So I’d say at least most of the water is going to the right place. So certainly it’s not a case where the sewage found a complete alternate path. The clog is in fact gone. Though there’s always a chance of leaks, which in this case would be into or below a concrete slab.
If I’m in this forum asking why my whole kitchen floor smells like sewage in a few weeks from now, plz remind me about this.
Maybe if I track down the MSDS it might say, but I can say for sure. The bottle is labelled as a pro drain cleaner for that purpose. So it’s not likely laboratory or military grade or anything intense.
Drain cleaners should be used very sparingly, especially if you have any metal pipes. What happens is they stay in the drain aRM and damage it, causing an eventual leak in the wall, or they drip down the vent stack at the intersection of it and the drain arm. That’s worse, because when the water does start flowing, it doesn’t wash it away, so it stays in the vent stack to corrode it. This is a particularly common mode of failure in houses built in the 50s, and it’s costly to fix because you have to rip out relatively large sections of wall.
Just something to think about.
Meanwhile, a plumber could have inserted a high quality camera to see exactly what was in there, then dealt with it using the bare minimum of force to not wear your pipes excessively. The cost of fixing the clog isn’t necessarily the cost of the fix. It includes the wear you put on your pipes that eventually causes a failure. Maybe your pipes are all great condition pvc and you have nothing to worry about.