The fact you have to say this speaks volumes.If I remember correctly, that was the exact same thing regularly (and correctly) trotted out by the previous Labour leader, and pointed to by his supporters as evidence he was the right person for the job.
Now those self same supporters are using the same line as evidence that Starmer is not the right person for the job - despite the fact it's them themselves who are prompting to say it. Starmer is correct too - he does still have the backing of most of the party.
A little bit of humility from the people who lost Labour the last two elections wouldn't go amiss. It's not the Labour party that elects politicians, it's the overwhelming majority of the country who don't belong to or have tribal allegiance to a political party.