In Shenzhen it's very unusual to have problems finding a taxi, but on our recent trip things were different. In Beijing you can stand waiting and watching those empty taxis zoom past because they're already answering a call. It was the same in Zhengzhou, Guiyang and a bunch of other cities.
So, if you're going to travel get DiDi on your phone, and if, like me, you can't read Chinese then get the English language version. Just search and find it. If you don't have a card linked you can only call a taxi by meter but it seems you can link just about any piece of plastic - my son linked his UK debit card.
It also solves the problem of telling the taxi driver where to go. You search your destination in English and it appears on his phone in Chinese. Happy travelling.