Stuffing up one set of tax cuts in a budget is forgivable, but it takes a special skill to stuff it up a second time in exactly the same manner. But to give full credit to Scott Morrison, he has done it.

Firstly in 2016, Scott Morrison took what was a pretty easy win on company tax cuts for small businesses and turned it into a fight on the ALP’s terms by including an unfunded and uncosted but clearly expensive proposal for tax cuts to begin eight years later for companies with a turnover above $1bn.

It allowed the ALP to turn the tax debate into one about equality and fairness, and those large business tax cuts remain stuck in the Senate.

This time around we have a series of income tax cuts – the first of which are an easy sell for low- and middle-income earners – but which Morrison has yet again combined with an unfunded and uncosted but clearly expensive proposal to begin in seven years that would see people earning between $41,000 and $200,000 paying the same marginal tax rate.

In a stroke it once again allowed the ALP to shift the tax debate onto its favoured turf of equality and fairness and immediately made it more difficult to get the legislation passed through the Senate.

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Is anyone actually advising the government?

Here we are less than a week after the budget and no one is caring about the tax cuts that are contained in the budget.

Where the government should be celebrating and talking up how they are delivering for low- and middle-income earners, they are instead having to explain how much it will cost to give a tax cut to people earning over $90,000 in seven years’ time.

It doesn’t help that Morrison’s own argument for the actual costed tax cuts contained in the budget doesn’t make much economic sense.

The two costed measures are for a new low and middle-income offset of $200 for those earning under $37,000, which gradually increases until those earning between $48,000 and $90,000 get $530, from which it then reduces until ending for those earning above $125,333. The second measure is to increase the 37% tax threshold from $87,000 to $90,000.

In his post-budget interview with Leigh Sales, Morrison explained the measures would help the economy because of the high marginal propensity to consume of low-income households. He correctly noted that, generally, poorer people will spend most, if not all, of any extra dollar they get, whereas wealthier ones will spend less of it (because they don’t need to). So tax cuts or benefits going to low-income households will generally be spent and thus help fuel economic growth (this same argument was used by the ALP during the GFC).

Morrison told Sales that the tax plan would strengthen the economy because those “on incomes of between 37,000 and 87,000 and those on middle and lower incomes, their marginal propensity to consume is almost 100%. That is why this measure, as the first stage of the personal tax plan, focuses on those households.”

Except the first stage of the tax plan does not actually focus on those households.

The increase in the low-income tax offset is something you only receive when you get your tax return. So those on incomes between $37,000 and $87,000, whose spending Morrison suggests will boost the economy, will only be able to do so after July next year.

The real first stage of the tax plan is the increase in the tax threshold from $87,000 to $90,000 because that starts from 1 July. Thus, by Morrison’s own argument, the early benefit is going to where it will do the least to improve the economy.

But putting the dumb economics aside, the plan at least was an easy sell. However, Morrison has lumped it in with the plan to remove the 37% tax bracket in 2024-25.

The costings for this measure are not in the budget; instead the government is meekly talking of the entire plan costing $140bn over 10 years. But the Grattan Institute has estimated that removing the 37% tax bracket will cost around $21bn a year.

That is a truly massive tax amount, the benefits of which all go to those earning above $90,000. For comparison, $21bn is roughly equal to the amount the government proposes to spend on both public schools and assistance to the unemployed and sick in 2021-22.

And so, once again we have a fight about tax being played out on the ALP’s favourite turf of equality and fairness.

But even more laughable is that because the government’s new tax offset is only payable after the next financial year, its threat of demanding the Senate pass the entire tax plan or get nothing is utterly hollow. Given the election must be held within the next 12 months, the ALP can deliver the offset at the same time, should it win government.

Here’s the Liberal party’s pitch to those who earn less than $87,000 – vote for us, or else the ALP will give you the exact same tax cut at the exact same time.

Except they can’t even argue that now that Bill Shorten in his budget reply speech has proposed increasing the new offset to $928.

But I guess one reason their tax plan is so full of holes is that the government’s real election strategy is not to talk about tax or the economy, but to attack Bill Shorten.

This week we saw government ministers attempting to be even dumber versions of Donald Trump by taking to calling Shorten Shifty Bill, and where Scott Morrison was repeatedly calling him “unbelievaBill”.

Sigh.

Unfunded and uncosted tax proposals and kindergarten-level name calling.

So much for the Liberal party heeding Malcolm Turnbull’s pledge to “respect the intelligence of the Australian people”.

• Greg Jericho is a Guardian Australia columnist