For network stats:
PoS difficulty is how chainweight is chosen. You are correct that the 90-day maturity effectively caps the attacker. You can still stockpile coin age, it just doesn’t help you attack the chain at all.
Maybe it would be best to compare using something like this: Peercoin, proud not to be an ICO. The PoW is more than just running your computer, ASICs are still involved, but the energy usage is something like 10,000x less and is done by essentially using the leftover ASICs from Bitcoin because they share a hashing algorithm.
Security depends on PoS difficulty. Higher difficulty = more secure. It’s just that PoS difficulty is not connected to price anywhere near as closely as PoW difficulty is.
Maybe a reference here to PeerAssets, or https://perpera.peercoin.net/ (Perpera Web Client v0.1)