You are implying that the current ad model, with a small number of high-value crafted announcements, doesn't work. I suspect it does. Gimlet has been pretty open about how their revenue exceeds their expectations and put them under pressure to grow their offering faster than planned.
It probably works for the listners, the direct advertisers and the podcasters. It doesn't work for the advertising industry as a whole because the middle men are cut out.
They want a cut and will work really hard to take it. L
I agree, I mostly hear ad's with promo codes on podcasts. The companies paying for the exposure know exactly what they are getting. It works out quite well as is.