The only thing that makes an evil “lesser” is that there is less energy going towards supporting it. By putting it into power you make it the greater evil. “Lesser evil” shit is something everyone has to unlearn if they are ever going to help anyone. How far capitalists and the state are willing to go is as far as they think they can get away with. If any capitalist or politician is being held back by morals, they will be replaced by ones that aren’t. If there is a profit margin to squeeze, anyone willing to squeeze it gains that power. People can get away with a lot more with less scrutiny, so the lesser you think their evil is, the more of it they can get away with.
The “lesser” fascist is still a fascist, and fascists spend much more of their time attacking us than attacking each other, and on top of that even if they do attack each other it’s through attacking us.
But the Democrats aren’t fascists, lesser or otherwise. They’re not ‘the Republicans, but less so’; they’re a different organisation with different histories and philosophies, different people and different priorities. The Democrats, for example, are not promising to overthrow the constitution, but overthrow it a bit less than the Republicans; they’re not planning to overthrow it at all. Degrees of evil are not possible in this case, nor in many others. The Republicans are straight up wrong in a way that the Democrats just are not.
For these reasons, I don’t buy the framing of lesser evil at all. If I did buy that framing, I would still wholeheartedly vote for the lesser evil, because it would still be better than more evil, by definition. Even your definition of ‘the same amount of evil, but slower’, would be better.
Further thoughts on this:
Criticising the Democrats as merely a type of Republican has other downsides: it effectively takes the Republicans as the standard type of politician, i.e., it turns every argument into an argument on their terms.
This also means that we don’t effectively criticise the Democrats, who are best criticised on their terms, not as merey lesser or mutated Republicans.