Dedicated servers for co-op are nice but are really not that important.

Dedicated servers are most beneficial when you have a good number of people connecting from multiple different locations. Since no one is host no one has a significant latency advantage and everyones client reacts similarly to whatever the dedicated server says, rather than everyone needing to react to whatever the host players computer says.

That's all super great for multiplayer pvp modes.

For co-op you'll have 1-4 people in a situation where someone having a latency advantage doesn't matter. In this situation having a host rather than a dedicated server will be a nearly imperceptible difference. There will be some situations where having a dedicated server will result in lower average latency for all players than P2P would get you and that will be nice.

Dedicated servers are nice but I think you're overstating their importance for co-op.