Is there a particular threshold of windmills to construct before we gain better control over earth’s temperature? I’m a little unclear what the victory conditions are in the fight against heat.

The threshold isn't measured in windmills, it's measured in co2.

If we emit more than 0, then we're in trouble.

Needless to say, we're in a lot of trouble.

The goal is not to "gain better control" over the earth's temperature, it's to stop actively throwing the temperature out of control.

Worth scrolling through this if you have been midwit-pilled into thinking humans have no levers of control on this question: https://xkcd.com/1732/

Please explain your alternative hypothesis.

They're not mills

It's kind of lucky for everyone that climate is mostly a perfect sliding scale, the more CO2 you avoid putting into the atmosphere the more heat capacity you'd avoid. So every bit helps. Many negative impacts of heat, like changing intense weather, biodiversity loss, and deaths to high heat also correspondingly change linearly with heat. So every bit is a literal victory, there's no major cutoff that we know of until things get really bad (which they might). What's your point?