Trump spent hundreds of millions of dollars officially, outside groups that don't need to report all of their spending (like the NRA) spent further hundreds of millions, and he had hundreds of millions worth of "earned media" due to the circus-like nature of the campaign.

Because he spent marginally less than Ted Cruz in the primary and less than Hillary in the general doesn't give lie to the premise at all. His 2020 reelection campaign spent ~$1 billion when including independent expenditures!