Unfortunately, Jackson is not actually that good at his job. It's not that he's not a good supervillain by himself. No, Jackson is a wonderfully genre savvy demigod with a wide variety of supernatural powers as well as biting wit. No, the problem is that Jackson is so impossibly arrogant and condescending that it is a wonder that he manages to keep a client for more than an hour. The subsequent books after this goes south for the first time are devoted to him having to do his own villainy as a result.
VILLAIN'S DEFEAT shows him dealing with the one thing he's never had to deal with before: failure. Jackson may be terrible at his job and been put on the ropes numerous times but he's never suffered an actual loss. Even if he did, he hasn't acknowledged it because his ego is the size of its own pocket dimension. His advisor, Sophia the Djinn, has been plotting his downfall for some time and proceeds to attack him where he's most vulnerable: his business.
Much of Jackson's power base depends on his villain consultation business, no matter how bad he is at the job. So once he starts losing his clients, he soon finds his divine powers fading as well as his ability to back up his claims to be the most superior villain of them all. Soon, he's scraping the bottom of the barrel and trying to help out the bad guys of a Robotech rip-off that even Jackson can't keep up on the specifics of.
However, it's a mistake to read these books for the plot. The books are best enjoyed purely for their nonstop stream of snark, sarcasm, and ridiculous over-the-top action. Jackson Blackwell is a distillation of internet commentators (without the racism) and virtually every page is full of him mocking everything from Star Wars' sequels to the MCU to older but beloved geek culture. If he hadn't gotten involved in supervillainy, Jackson would have made a wonderful Youtube commentator.
Part of what makes these books so entertaining is they're not afraid to cross the line twice. At one point, Jackson sends a bunch of orphans to a child-eating witch but they get rejected. This results in them becoming a feral tribe of would-be supervillains trying to get Jackson to adopt them. Then Jackson sends them away to become superheroes so he can kill them as adults. That's the kind of humor we're dealing with (and I'm not even mentioning the "present" they gave him).
Check it out and if you love black humor, arrogant anti-heroes. as well as mockery of popular media then you'll love it. I do have a small complaint about the book ending on a cliffhanger but that just means I'll be picking up the next one first day.