Can you explain/expand your reasoning behind that a little more? This is the first I've encountered such a point.

Tax pyramids occur when the total value is taxed at each point of sale instead of the value added. This results in taxes being taxed which effectively increases the tax paid on earlier stages. For example, very few would find it reasonable for a 100% excise tax to be applied to alcohol or automobiles but less would object to a 30% tax and legislating a certain structure for the sale of alcohol, for example farm -> brewery -> distributor -> retail or manufacturer -> dealership, that effective results 185% or 69% whilst only having the appearance of charging 30%.

The easiest and most effective way to reduce this tax burden is simply expanding your vertical. This is why tesla is so staunchly against third party dealerships or why hyperscalers and apple, google, microsoft, and amazon are all starting to make their own chips. Breaking up big tech won't accomplish anything in the long term without fixing the broken tax system and the incentives it creates.

Progressive corporate taxation?

I'm curious about how "pyramid shaped tax structure favors vertical integration". What is a pyramid shaped tax structure? And what about it favors vertical integration? Casual searches on it don't yield much great info atm.