The position of a radical skeptic is that absolute knowledge is impossible. Agrippa's Trilemma doesn't help your case. In the trilemma, one position is that there are inherent truths. This is not true, as who decides the inherency of truth?
No one opinion is more valid than another. The second way that knowledge is supposed to be possible is through the infinity of proofs. David Hume established the the link between cause and effect is illusory. Any proof that is attempted through that is wrong. Why is each proof connected to the next? Because we decide so. There is no other reason but human wishfulness to connect axioms. Thirdly. A way to justify knowledge is by saying the proof backs up the theory and vice versa. This is impossible as proof can never support theory. One thing can never justify another. Trees fall down when they are cut, why? Gravity? How does gravity make a tree fall down? Because that is what gravity does. Why does gravity do that? Because it does. When intertwining proof and theory down to the elementary level, an absurd, unprovable statement will arise.
Agrippa's trilemma is not trying to say there are different kinds of knowledge, it is trying to point that trying to JUSTIFY knowledge leads to one of the fallacies (which you outlined as though they were a rebbutal to agrippa's trilemma).
Agrippa's trilemma points out the fallacy of trying to justify knowledge. We are trying to classify knowledge, not certify it.
The reason agrippa's trilemma shows that the radical sceptic is wrong, is because the radical sceptic believes that any kind of knowledge must be justified by one of the trillemma's therefore falling into the same trap that justificationists do, i.e believing that the only type of knowledge is knowledge that is justified which is false. The difference between the people who believe that justification is necessary
is like this
Finitists believe that the infinite regress is legitimate
Axiomatics believe that there are self-evident truths
coherentists believe that things can be justified by themselves.
Radical Sceptics deny knowledge is possible, because none of the above work and the only true knowledge has to be based on one of the above. they don't reject the idea that one of the above would factor into "true" knowledge (which they should, in other words knowledge would not need to be justified.) they instead state that knowledge is impossible (which is false).
That is why agippa's trilemma helps my case.