Why would Johnson be behind someone from Doncaster Rovers? Johnson has 4 goals and 4 assists, James 7 goals and 2 assists(according to WhoScored). James might have got 3 more goals but he is playing in the division below and has started twice as many games, playing over 1,400 more minutes than Johnson this season.
Corey Blackett-Taylor has managed 8 starts for Tranmere. 3 goals and 1 assist in League Two.
I don't know an awful lot about either of these two players but I don't really see how they would be an upgrade on Marvin Johnson?