The notable exception to this, of course, is Trump's primary AND general elections.
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!
It's weird that people believe he is a political outsider. I've never heard a holistic/logical argument showing he is somehow more divested or decoupled from the implicit oligarchy class that ultimately is deciding legislation/law/executive orders these days.
I guess it's because he's bounced around parties and people are really firmly sold on the republican/democrat binary, seems superficial to me but I'd be willing to hear any cogent argument made.