I don't know if you read your own source but it's incredibly unconvincing "research" slop. In their "case study" they just point to a particular race and the money the candidates received and infer it's bad.

No analysis if the politician was acting against their constituents interests... Pretty embarrassing paper to put their name on. I can see why there's no coauthors.

Also they conflate political ad spending with issue awareness ad spending, which is a borderline malicious.