Do you believe in the effects of media?
More specifically, do you believe that different channels impact people differently and that the effects can be measured?
If yes, then 'media agnostic' isn't the right approach since that means 'without knowledge' or more generally something that can't be proven or the individual has no proof and thus ends discussion.
Defining audience targets and then building appropriate media plans for a desired experience outcome absolutely requires understanding how different channels work and interact (like radio impacting awareness among Internet users.)
What we need is more information, analysis, and proof about how things work in the real world.