I think it dates back to their succesfull junior era, when Babos and her team said Timea is the more talaneted player between the two
Back then they were talking some BS, like Timea having a top5 serve and her FH is fixed now, its like Nadal's FH
Probably there are no evidence for these, or one should dig really deep in the internet, but i remember vividly, cuz even back then i thought wtf.