"just as badly as" is correct and usable in written English, and it could be used in a variety of contexts.
For example, "He missed the train just as badly as his friend."
The Midshipmen still want to beat Army just as badly as Army wants to beat them.
If not, they will be tossed about just as badly as everyone else.
Oil producers need to sell just as badly as customers need to buy.
So-called pure-play online drug retailers may have stumbled just as badly as merchants in many other Internet categories.
"There were women in Enron who were in the club and behaved just as badly as the men.
"I think the reason teenage fiction is so popular with adults is that adults hunger for narrative just as badly as teenagers do," says Ness.
"Black" and "Asian" identities are just as badly bolted together as anything else.
He recalled: "I had only one brain and it worked just as well, or just as badly, no matter where I was sitting.
Netflix has tried to make itself appear more magnanimous than it actually is, the result being that staff are now probably just as badly off as they were before.
Millions of young men and women sit in freshman composition classrooms each fall semester, but if the Arum report is right, nearly half will write just as badly in their junior years as when they started college.
Tory candidates losing deposits in byelections under John Major's premiership performed just as badly in safe Labour seats such as Monklands East and Barnsley East but had the good fortune not to be beaten by strong fringe candidates.
