Very few if any, petrol tanker work has always been at the very much higher end of HGV driving pay scale wise along with generally far fewer hours.
You’d really have to be a bit daft to swap one for the other.
Can’t help but agree with that, there was no such thing as an ADR when I was in the trucking game, just an HGV licence with various groups, I had a group 1, which covered all groups up to and including articulated vehicles, but oil companies would train you up if you weren’t familiar with loading or discharging oil, and all the tanker driving jobs I ever did paid bundles more than running about with either containers, or a curtain side trailer.