Yes absolutely correct a centrist Labour government would never win power and certainly never win power three times would they? Oh but wait........
Now I wonder when a left wing Labour government last won an election?
You both have a piece of the puzzle each, but, as put, I agree -- doesn't it make the Tories more electable not Labour? Cameron's, like Tony's, legacy and programme in the party wasn't secure when he departed. Moreover due to recent political events, both contesting ideologies in their respective parties had got a free pass to reassert themselves with mixed results. Arguably, May and a few fundamentalists did a better job; whilst Brownites and Milibandists floundered, allowing Corbyn to come through as a political passenger more than a leader with a programme in his own right. Neither party is fully united, or ready, and silly populism is rampant; hence there's a false sense of confidence either side of the political spectrum. I don't share it. Sadly, only one force can benefit by default at present -- the incumbents in power.
Indeed, neither the immigration rhetoric from Umunna and Reeves (if they go down that route, it'll be worse for them than the fees issue for the Lib Dems) nor the budget from McDonnell (with Mason's at times unhelpful interventions from the sidelines; some of what he says is Labour policy, but not all of it) sound very coherent or convincing. Even if the calculating Blairite mind is there on the former and Labour's heart is there on the latter, without a clear and organised communications strategy -- let alone policy work and evidence -- these will be taken apart quickly by internal and external opponents. They have four years to shape up, with any luck.
Now, to unite and actually do something productive, I believe Labour must choose either the social or the economic axis to attack on whilst accepting compromise on the rest until Brexit is complete. Doing either too much or too little, giving ground to the lowest prejudices of the public, will be equally disastrous.