If you go back to '74, gubernatorial elections are pretty similar in distribution to the Presidential since '76, but with less recent strength; you've got a narrow Dem majority in '74, a plurality win by a Democratic in 1990, and a lot of big blowout wins by Republicans, with all but one after 1994 being 10-point or greater margins ('98 was over 30 points, 2006 was a hair under 10 points, but it was also a weird four way race.)

“~50%” as the typical Democratic share of the vote in Texas requires a generous interpretation of the approximation symbol.