When you spin up a new node, you are not merely downloading the blockchain. Your node is re-living the entire history of bitcoin, validating every transaction, block, and fork.
Discussion
True. Having the data doesn’t alleviate your need to run the verification.
The way I’m thinking about it is like having a very fast peer. So you still initialize your node as always, but you have a super fast peer right next to you feeding you historical blocks.