> Hydra is “about as close to the Cardano L1 as you can get with an L2”
I don’t agree with this. In what sense do you mean? Economic activity on a Hydra deployment does not directly translate to economic activity for Cardano. Whether you do ten transactions or ten million transactions does not necessarily impact the fee revenue earned by the Cardano L1. The L1 benefits from fees in Hydra: when the head is first deployed, when funds are deposited to the head, when funds are withdrawn from the head and when the head is closed. This means that activity within a deployment (ie transactions in a Hydra ledger that are not deposits or withdrawals) do not interact with the Cardano L1 at all, and thus do not generate fee revenue for the network.
Economic activity on Midgard directly translates to economic activity (and fee revenue) for the Cardano L1. The more transactions in a Midgard block, the higher the fees that Midgard will have to pay (to the Cardano L1) to publish that block. It’s not just deposits and withdrawals that product fees for the Cardano L1, every single Midgard transaction results in fee revenue for Cardano.
> “Hydra primarily relies on Ada as a token and the Cardano L1”,
Again in what sense? There is no requirement for a Hydra deployment to charge users fees in Ada. What participants charge to users is entirely up to them. In practice, if you look at the Hydra apps built to date, the most popular architecture is the delegated participant topology. In any such Hydra app, it’s up to the participants to determine what they charge for fees, there is nothing that requires this to be Ada. Even more so, the state of a Hydra deployment does not live on Cardano, it is an offchain ledger managed by the participants of that deployment.
Midgard relies exclusively on Ada as the fee token, and the state of Midgard (ie the Midgard blockchain) resides entirely on the Cardano blockchain. It does not exist independently, the state of Midgard is literally a chain of blocks (each represented by a UTxO) that lives on the Cardano L1, when a new Midgard block is produced, a new “block” UTxO is appended to the Midgard “blockchain” on the Cardano L1. The only way state on Midgard can progress is via the Cardano L1, if nothing is done on the Cardano L1 than nothing can happen on Midgard, the same is not true of Hydra. You can progress the state of a Hydra indefinitely without ever interacting with the Cardano L1 because the ledger is maintained offchain by the participants, the Midgard ledger on the other-hand is entirely maintained by the Cardano L1.
> hydra doesn’t have its own nodes.
Hydra does indeed have its own nodes that are distinct from Cardano nodes, each head participant is a node.
Hydra is great and is an incredibly powerful protocol that has the potential to enable a plethora of completely novel decentralized protocols unique to Cardano via interconnected Hydra head networks, but it is in no way “more closely tied to Cardano than Midgard”.
It is impossible for Midgard to “vampire attack” Cardano because Midgard is a protocol that exists entirely on Cardano, value in Midgard does not “leave”Cardano, it just lives at the Midgard smart contracts on Cardano and all activity on Midgard directly results in economic activity on Cardano (as any progression of Midgard state requires transactions which interact with those smart contracts, which again, live on the Cardano L1). There is no Midgard without Cardano, it is entirely dependent on Cardano in every single aspect.