In all the recent debate about cuts and deficit reduction, one question that should perhaps be asked more is: dude, where's the opposition?

The Labour party's leadership contest has so far failed to generate much excitement, which is not so surprising given the air of inevitability that is gathering around it lately. It now seems all but certain that David Miliband will be the next Labour leader, which is a shame – because a more promising candidate has been almost completely sidelined. That candidate is Andy Burnham.

Of all the hopefuls, Burnham has the most distance from the still-toxic legacy of the New Labour project. This has allowed him to be overtly critical of the "factionalism and indulgence" revealed in Peter Mandelson's book, which is rapidly becoming shorthand for the New Labour-style of government. Conversely, Ed Balls and both Miliband brothers were all key – albeit junior – members of the Blair and Brown teams, so right at the nucleus of government for the last 13 years.

There is something dispiriting, and predictable, about automatically promoting the assistants when the bosses have left. It's what tends to happen when no one else applies for the job – much like when Gordon Brown himself got an uncontested promotion in 2007, to lukewarm applause all round.

Diane Abbott is arguably the most left-leaning of all the candidates, but her lacklustre pitch so far has mainly consisted of repeatedly pointing out that her opponents are all Caucasian men. Recently, she varied the riff by calling them "geeks in suits". When she does present an argument, it usually comes across as half-hearted, presumably because she knows that she won't really get the job and is now just going through the motions.

Burnham's big idea – "aspirational socialism" – is too oblique to try to interpret at this point. Like the "big society" before it, it's still only a gift-wrapped package with an only vaguely discernible shape. "Socialism" is a concept in urgent need of a brand detoxification, to be sure, and it seems a risk to even have it on the platform at all. But it's canny to weld it to "aspiration" – it'll hopefully reassure the public that this isn't a regressive, totalitarian sort of socialism, but one more in tune with the zeitgeist. If that seems reductive, it's because soundbites are, but they're no less significant for that.

In policy terms, Burnham is more explicitly socialist than aspirational, but he still stays reassuringly within a centre-left, moderate framework. In summary: he wants to introduce a financial transaction tax, uphold the 50p tax rate, support the future jobs fund and introduce a national care service for the elderly. His could be an antidote to the ultra-liberal path taken by the coalition, just stopping short of the scary sort of big-state socialism. It's exactly these sorts of arguments that Labour in opposition need to be making, and Burnham is, I would argue, the best placed of the five contenders to put these arguments forward.

One consequence of Burnham's marginal role in the race so far is that we haven't seen him properly tested yet, both in terms of argument and presentation. He comes across as earnest, perhaps even a little po-faced at times. He makes a point of frequently mentioning the "London-centric" politics of his peers in all parties, a difference underlined by his own Merseyside twang. If he became leader, this may play well in differentiating Labour from the overtly metropolitan, RP-speaking government ministers. In the short term, it also differentiates Burnham from his overtly metropolitan, RP-speaking opponents for the party leadership.

There's every reason to think that by 2015 the honeymoon will be well and truly over for the Lib-Con government. The planned cuts will have taken their toll and the novelty of a coalition will have worn off. It seems safe to predict that the Liberal Democrats will be hemorrhaging left-leaning voters. Labour, on the other hand, will have had five years of the relatively easy life of opposition, criticising the government without having to expand any fully worked-out alternatives. In that time, Burnham could have a chance to shed his ingénue image and gain some PM-like gravitas – and after that, who knows?

Unfortunately, the current Labour big beasts don't agree. Jack Straw, Alistair Darling and Alan Johnson have all thrown their lot in with David Miliband. Financial backers have followed suit, with Miliband the elder raising six times as much money as the second most-funded candidate (Balls), and more than 100 times more than the least-funded (Abbott). Even if he turns up clutching a banana in each hand and grinning ear-to-ear at the party conference on 26 September, David Miliband still seems set to walk it.

It's partly this kind of "who-else" appointment that made the previous Labour government seem insular and unresponsive. It would be a missed opportunity if the Labour party continued in the same vein, especially when a proper, credible opposition is needed more than ever. That's why Labour need to give Andy Burnham more room in the limelight between now and the conference.