Well the main problem is that they probably aren't actually putting tax cuts on things that are shown to have a good ratio of fiscal stimulus for the dollar spent.
e.g. if you look up fiscal multipliers, then several sources state that the highest one for any tax is payroll tax. e.g. each dollar given back on payroll tax creates the most growth possible of any dollar given back. And it's kind of obvious why it would do that, since cutting payroll tax makes it more affordable to hire people, allowing businesses to offer higher wages and bring more workers into employment, while also giving workers more money to spend. It's a win-win, and it's obvious why it would work and give across-the-board benefits.
Yet, why don't they even include that in their cuts? Since I assume they aren't just morons, then I have to conclude that growing the economy isn't actually a goal they care about. What they care is that their donors are able to maximize their slice of the pie. This could end up as a real threat in "post expansion" capitalism: if the ultra-wealthy basically maneuver to have the biggest slice of the pie, even if that means shrinking the pie. And sadly that seems to be exactly what they want to do.