Prime Minister Malcolm Turnbull might do well to try to keep Andrew Robb on as Trade Minister for as long as possible. His departure will weaken cabinet at a point when Turnbull needs all the experience and good sense he can get.

One of Tony Abbott’s pitches in the lead-up to the 2013 election was that he had a team with ministerial experience from the Howard years. This made a virtue of the fact that he couldn’t bring himself to cut out dead wood like Eric Abetz, Kevin Andrews and Bronwyn Bishop, but there was an element of truth to it — Joe Hockey, Julie Bishop, Malcolm Turnbull himself and Abbott had all served as ministers under Howard. Turnbull, however, took the opposite approach, hacked out the dead wood and rusted-on Abbott supporters and went for new talent.

The result is a cabinet with a handful of experienced ministers and the rest relatively inexperienced. Scott Morrison, in particular, has visibly struggled in the Treasury portfolio, having discovered that demonising refugees and hiding from scrutiny was a poor preparation for running fiscal and economic policy. When Morrison travelled to Perth so that Finance Minister Mathias Cormann could hold his hand for MYEFO in December, it spoke volumes about the relative capacity of the two ministers. Cormann was one of the few stars of the Abbott government, adeptly handling a complex privatisation process. Julie Bishop and Andrew Robb were the other two successes. Whether Robb actually believes the long litany of bullshit he has been offering about the benefits of preferential trade agreements over the last two and a bit years, he has gone about the task of signing them off with alacrity, providing the only successful component of the Abbott government’s economic narrative.

Robb, as a former federal Liberal director, agri-economist and a successful board director, also brought substance to the Coalition, even if the leadership ambitions he harboured might never have been realistic. He was also a strong counterweight to the xenophobic attitude to foreign investment harboured by the Nationals.

But now, Barnaby Joyce, arch-opponent of foreign and particularly Chinese investment, is likely to become deputy prime minister, leading the Nationals in an even more investor-unfriendly direction, while Robb will be finishing up his career in politics.

It’s an unbalancing that Turnbull, and Australia, don’t need. It’s difficult to understate just how economically dangerous Barnaby Joyce is. He holds views far outside mainstream economic orthodoxy, not merely on foreign investment but on fiscal policy (remember his warning that Australia was going to default, when our net debt was a fraction of the size it has grown to under the Coalition), climate change and agricultural policy. As shadow finance minister under Tony Abbott — an appointment that shocked and dismayed Liberals — Joyce had to be dumped as his comments on investment and debt became ever more wild and damaging, not merely for the Coalition but for the economy.

As deputy prime minister, even if he is confined to the backwater of agriculture, his toxic mix of crass populism and agrarian socialism will carry more weight, and he will speak with the authority of party leader. A Joyce deputy prime ministership will be bad news for foreign investors, especially if they’re from China. And there’ll be no Andrew Robb to counter him within cabinet, to confront like-minded media allies like Alan Jones, to make the case for the benefits to Australia of foreign investment. This will have consequences in terms of investment, in terms of jobs, in terms of growth — none of them good.

It also means Turnbull’s cabinet will tilt decidedly in favour of inexperience, with a new National coming in while Robb clears his desk, and replacements for Jamie Briggs and, perhaps, Stuart Robert to be found, while Mal Brough continues to circle in limbo. Meantime, the Abbott forces will continue their destabilisation — notice how Abbott unsubtly made a point of dragging Morrison into the story of Robert’s 2013 dinner for Chinese businessman Li Ruipeng. Morrison’s failure to make the most of his treasurership and his missteps on the GST compound the problem.

Whatever plans Turnbull might have had for the first parliamentary fortnight of an election year have been blown away by his frontbenchers. At this rate, the shiny new Turnbull government of last September is going to be a battered wreck by the time it gets to an election in the second half of the year. Perhaps Turnbull really should go early rather than wait for more ministers to hit the fence.