Banning PoW cryptocurrencies is not a big enough priority for anyone that it will be a motivating factor to move past the other issues surrounding the climate debate, especially not anyone on the side of "don't do [thing] to fix the problem". I don't see any other mechanism by which it makes passing other climate legislation harder.
Banning PoW cryptocurrencies removes money that is currently on the side of "don't pass climate legislation because it will harm my PoW cryptocurrency business" from the table. That makes passing future legislation easier.
In general, trying to solve all the worlds problems at once doesn't work. It's too complex, you paralyze the decision making body with too many tradeoffs. When something is obviously bad, banning it immediately not only has the effect of meaning it's gone immediately (and doesn't hang around until you solve the whole problem), but it simplifies the remaining problem for the decision making body. This makes them more likely to come to a consensus on exactly what to do in a finite amount of time.
Does it? And, do you have data that backs this up? It stands to reason to me that PoW miners only want cheap power; they don't really care too much how it gets generated. Considering that the cheapest power source you can build out today is green energy, it sounds like a win-win to me for them to put their money into "advocate for more cheap power."
If we won't legislate it now, it's possible we won't get a chance to do it later thanks to bickering from lobbyists and fossilised laws and practices. See IPv4.