I think you're seriously underestimating young Mr. Walker. He's shown a freakish level of athleticism and body strength. He's shown a willingness to commit to putting effort in on D. He's only 20 years old. He's shown flashes of a jumpshot and midrange game. He is a devestating slasher who can get to the hoop. He also rebounds strongly... His game is not very polished, but there's very little wrong with it. He's also shown significant mental toughness, coming back from significant injuries, and he raised his game in the NCAA tournament at crunch time for his team... His at ude problems appear no worse than those of SJAX, and he was really useful...
Also, Batum is, IMO, not ready to come to the NBA now. Bill Walker could survive limited minutes and develop as he went.