User blog comment:B214/Volume 22 spoilers/@comment-95.90.227.243-20160720115334/@comment-1359322-20160720120624

First Vali is already a High-class Devil, just like how Rias, Sona, Riser, Sairaorg and so on are all High-Class Devil from birth. So what's the point of promoting a High-class Devil into a High-class Devil?

Second, Super Devil isn't a class, it's just a name/title they give to Devils with irregular power.

Third, Vali has more years of experience to him than Ise in regards of using their power and fighting, of course Ise would be weaker than him currently. You can't expect someone who only started using his powers 6 months ago with someone who has been using it for half of his life. This is the same with how neither Vali or Ise can beat the first Sun Wukong yet despite surpassing him in power. Also remember Vali doesn't solely rely on his talent, he trains just as hard as Ise does, so it's natural that he's one step ahead of Ise in terms of powers at the moment.