My thoughts is that this is how Reform get in. Until we rid ourselves of FPTP, splitting the left vote so much means a Reform government. Until such time, we have to vote tactically. Vote to keep out the worst. Perfect is the enemy of the good.
If Labour put country before party, they would be killing of FPTP like the membership want.
Labour have a good few years to get themselves together before an election.
I agree they are unlikely to do what the country needs, and membership wants, with voting reform. Maybe if they are sure they will lose and Reform would win. Doubt it even then though, because "we might still win".
If everyone can agree on another left party fine, but it will be split over Green, SNP, LibDems, Plaid and Labour. That's how we, a left leaning country, get endless right wing governments and their madness.