I wouldn't mind being a Physics teacher.
Oh yes you would!
I think you are labouring under the illusion that, as a 'physics teacher', you would be teaching physics.
The pay isn't the main reason people aren't joining or staying. It rates around #5 on the list.
Remember, increasing STEM teacher skills and numbers has been officially the top DfE
PR campaign for 10 years, with nothing but a drop in same as the result.
PM me if you want the gory details. Ditto school leader, though CharlieGolf has a the experience there, and will tell you the same thing.
You point about salary, according to what I've read, does apply to TG4 however, as does the point about not doing the job you thought you'd be doing.