Essentially every winner-take-all election comes down to the establishment and the opposition. Either you like the team in charge and vote for them, want them replaced and vote for the most likely challenger, or find both choices equivalent and do something else with your vote.
NYC's mayor election is a great example. Every adult who looked at polling knew that it would either be Mamdani or Cuomo, and those who still voted for someone else were communicating very effectively that both choices were equivalent to them.
Look, you can do whatever the hell you want to with your vote. Spoil it, waste it on a "third party" vanity campaign, or just skip the election. Just don't pretend that your wasted vote is somehow not a declaration that whomever wins is as good to you as the runner up.
Cuomo, who was endorsed by the outgoing mayor, was the establishment. Mamdani, who ran an insurgent campaign to beat both Adams and Cuomo in the ranked-choice primary, was the opposition.
That the choice was either Cuomo or Mamdani was so obvious that the leadership of the Republican party endorsed Cuomo over his own party's nominee.
The DNC primary was not a winner-take-all election. We could call them "single ballot plurality wins" or "first past the post" if the difference is confusing to you.
Where the fuck did I say that? Go ahead and waste your vote all you want. Sometimes both plausible winners suck, and "they both are equally bad" is a perfectly fine fucking message.
Just don't expect any rhetorical accolades for voting "either" from the rest of us.