It's somewhere in the middle. Ex: there isn't a literal potash or nitrogen monopoly, since it's a worldwide market. There is arguably an oligopoly on some levels, and then at the producer level you can see some OPEC style arrangements.

They are at the bottom and the players above them have leverage on every level. Unfortunately the way for them to gain power at the base level is to consolidate and grow - agriculture mega-farms - but that's something there also strongly fighting against.

Ultimately smaller farmers probably need to be some sort of protected class, which they already sort of are, but not to a proper extent to ensure their survival as they argue. This is the state of things in many countries in the world now, which is something that they see and accept but do not necessarily like, but that won't change policy in regards to Indian dairy Farmers or what have you so there's little prospect except frustration. Even in aggressive trade negotiations with tariffs flying over the seas at full bore, things like fishery rights and such often turn out to be the most steadfast holdouts. Not easy to change.

Or perhaps the trend of consolidation will simply continue, and there is an imminent wave of small farm bankruptcy.