The basic income amount in our policy is at least two years out of date, because I have failed to update it. So the 14K should come with a pinch of salt and a promise (on my part) to correct it this year.
The chief benefit of the job guarantee is that it offsets the worst side effects of the NAIRU. The NAIRU (non-accelerating rate of unemployment) is a concept used in monetary policy, and essentially says interest rates should be used to ensure that full employment can never be reached. If the unemployment rate gets too low, interest rates get cranked up in order to slow the economy down. This is how monetary policy works today. Keeping a so-called "buffer stock" of people perpetually unemployed means that wages can be kept down for everyone else. It is a calculated intervention in the economy by the authorities to rig the game against wage labour. And it mostly goes on unnoticed.
Many countries who brought in NAIRU also brought in offsetting measures such as more income redistribution and universal healthcare, but it's never really been enough. And there has been a lot of welching on the social compact, with the social wage being eroded and governments actually abusing/targeting the very people they have forced to be unemployed, purely because they are where government policy has put them.
So there is a strong moral argument for a job guarantee to offset the impact of forced unemployment. But there are also many practical issues on the implementation side and several ways in which a job guarantee could be done. The ideal policy in my view would be to propose a trial of several different job guarantee approaches in different disadvantaged communities, with intent to collect data and allow the most successful models to spread and be adopted elsewhere. An evidence based party has to be guided by evidence. Full rollout of the idea would be an end outcome if the concept works in practice, isn't rorted and doesn't become a vehicle for bullshit jobs.
You could also go even more radical. Abolish NAIRU altogether and if inflation threatens, increase interest rates or levies on land only, and then allow land sales to the state at a fixed price. In effect, contain inflation by the suppression of land prices rather than wages. This is another thing that might not work in practice, but might nonetheless be worth testing. We aren't living in stable times, which means we get to think a little bigger about what is or isn't possible.