Yes true. About same pay, but SLK has bonus, insurance, crew meal, the usual goodies.
On the other hand, you do not fly very much in SLK, that's why you earn less. If you are western nationality you feel more at home in TGW. After a few years you do not want to go to SLK, to avoid going sideways. But as I said, you want maybe join SQ/SQ Cargo afterwards.