They're basically saying "If we continue to emit as we've done, things will become less cozy than they're now", right?

I'm not claiming that everything "they're" saying is true.

But your rebuttal is just not valid.

It's like saying: "They pretend to be able to predict the overall temperature of this gas in this cylinder which gets heated up locally by a coil. And yet they can't even accurately predict the local flow and temperature in the short term." Not a valid critique.

If their claim, that the atmosphere is overall getting warmer, is true, then it's quite reasonable to assume the the frequency and severity of weather extremes is going to increase.

And no, accurate weather forecasting is not a prerequisite to come to this conclusion.