I don't think he means that the important difference is that today's economy is low growth, rather than today's economy is post-industrial. The US economy of the 19th and 20th century was largely and industrial one, accompanied by substantial territorial expansion. Therefore, one should not expect any policy to produce 19th century growth rates in 21st century America.
Well, then it's a strawman, since the argument in favor of income tax cuts is not that it will produce 19th century growth rates (were those even high?), or any particular growth rate. It is only that they will lead to higher growth rates than we currently have.
It has always astounded me how traditional rational-actor economic theory continues to produce statements as divorced from reality as "Income taxes in particular provide a disincentive to work." Here in real life, regardless of the tax rate, people need to work because they don't want to be destitute. Whether they're taxed at 5% or 40%, work is still better than no work: better a slice of the pie than no pie at all. The tax rate has absolutely no effect on the amount of work I do. That is influenced by other factors - like how much work I'm able to get, family commitments, whether the work is worthwhile and interesting, the bills that need to be paid.
It depends on your particular situation, the difference in marginal tax rates that you're facing, and whether or not you fully appreciate the amount of taxes you're paying. I am very cognizant of tax rates, and when marginal rates went up a lot for me in 2013, I actually turned away business because I didn't think it was worth my time. I also spend a lot more time thinking of ways to manage taxes, both for myself and my clients. The Obamacare taxes on investment income really altered the investment landscape for affluent people quite a bit.
At the lowest end of the wage scale, implicit marginal tax rates are very high and create a huge disincentive to work. That was the main factor in the loss of jobs due to Obamacare predicted by the CBO early this year. The income-dependent phase-out of subsidies resulted in a 15-20 point increase in the marginal tax rate for those receiving subsidies.
I agree that for most people a 1 or 2 percentage point change in marginal tax rates won't change how much they work. Still, when averaged over the entire population, the effect is probably noticeable. Remember, many of the metrics of the economy reported in the media and by politicians are only fluctuating by a 1 or 2 percentage points. For example, 6% unemployment is bad, but 5% unemployment is great. Real GDP growth of 2.5% is good, but 1.5% growth is sluggish. You think a reduction in your take-home pay of 4% is not enough to make you work less, but would you really notice if you worked less by 1 or 2% because of it? Or quit that job a little earlier than you would have, or took a little extra time between jobs to travel?
But hey, the big incentive here is to hire an accountant and take advantage of the loophole. I wonder if it is actually possible to structure a complete range of jobs as distinct businesses. Subcontractors for stocking shelves at Walmart?
Not a bad idea, but the state probably requires that you pay yourself a plausible market level wage, so unless you make a lot more than that, it wouldn't help.