I think we need to get a better handle on definitions of Perseverance, Work Ethic, Desire etc.
I don't think it's a balance of one or the other. Perseverance is not the opposite side of the same coin as what people are describing as work ethic. Desire, isn't the same as perseverance and it's not the opposite of work ethic either.
Personally I think work ethic is not a trait, but more a bundle of traits, or how a bundle of traits dogifest themselves. So some of the traits that go into both of these are likely nearly completely genetic, and some have a greater environmental aspect. However, I don't think there's any kind of consensus on what work ethic is in a dog, or even if it's possible for a dog to have it. Work ethic is belief in work as a moral good. Pretty sure dogs don't have that. Instead they act in ways that seem similar to how a person with a good work ethic would act. The motive for a dog isn't because it's a moral good at least I don't think it is.
All high drive dogs are not on the edge. All dogs that have perseverance are probably high drive dogs. Perseverance is the good part of that high drive. A dog can't have too much of it. Same thing as what most of the folks on the thread have described as work ethic. You can't have too much of it. It's not a soft dog, it's not a dog that isn't capable of independent work, it's the good part of what makes up a dog that wants to work with you. Someone earlier described it as a dog that doesn't get down while doing T work or some of the other boring to the dog drills etc. It's a dog that seems to try extra hard to do what you're trying to get it to do, and doesn't lose confidence if that takes some time for it to figure out. So dog maxed on perseverance and work ethic would allow you to harness that perseverance. I don't want less perseverance, I want more work ethic, whatever that is.