I don't understand why Bitcoin is more decentralized than Ethereum even though you operate a full node with both.

To create the blocks:
Bitcoin PoW = miners
Ethereum PoS = Validator

With Bitcoin/Ethereum Full Node you can verify the blocks from the miners/validators.

So the only point why Bitcoin is more decentralized than Ethereum is:
The Bitcoin Full Node is cheaper than the Ethereum Full Node ?

Or is it the case with Ethereum that you cannot verify the blocks as a full node but only as a validator?
So:
Bitcoin miners create block / full nodes verify the block
Ethereum validator create block / validator also verify the block