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
You probably need to learn the basics. I also suggest reading the blog made by a person who calls himself "StopAndDecrypt". His writings are technical, but easy enough to read for newbies to learn and understand.
Here's one of writings that's relevant for the topics that you're asking about,
https://medium.com/@StopAndDecrypt/266c136fc55d#aee4You'll learn what nodes actually are, scaling, and other related topics that all Bitcoiners should know/have a minimum level of understanding.