It sounds like you got hold of a poorly cared for kart. Any kart that has flattened frame rails is going to be a crapshoot.
When I ran Exprit, we had a 2014 kart that had an entire season of brutal national racing on it. I got into a big wreck at a big race and cracked the frame. Fortunately, we had a new 2014 kart on-hand, ready to go. We set that one up and went out and set times within a tenth of what the other kart was. Kart felt no different.
Don’t discount one brand because of a bad experience. Of course the kart won’t last indefinitely, no kart will. But if you care for your stuff and keep it clean and run skid plates, you could easily get a season or two or more out of an OTK kart. I’ve seen it done.