I still don't see how they botched him. He was trapped in the Quantum Realm without his suit. Once he got his suit, he took over, amassed a giant army (no pun intended) and was ready to invade Earth once he got his power source out. Even the resistance at the end was being slaughtered by Kang.
I mean, was it the ants? I got it- the ants, as they fell into the quantum realm, experienced hundreds or thousands of years of evolution, until they were just as technologically advanced as Kang. So of course they could find a way through his shields. Then in the final fight, Kang was kicking Scott's ass- it wasn't until Hope came back that they were finally able to beat him.
Here's a question for you- if Scott and Hope had been stranded in the Quantum Realm, if their defeat of Kang had that sacrifice, would you still think Kang was nerfed?