I dont believe the FCC allows a candidate to buy out all available time. If a broadcaster sells 5,000 spots to a candidate, the broadcaster must allow other candidates to buy an equal number of spots at the same rate.
What gets squeezed out is regular advertising, and the commissions that sales people get.
Also the way it is shaping up, only Biden and Butt and Bernie can even spend a high fraction of that amount. My understanding is, this $37-38B buy is just to nail down prime in the top DMAs, and as I noted, that is extremely easy to do in 5 or 6 of those states.