Decentralization is a spectrum. A truly decentralized network, one pure from every angle of analysis, does not exist.
Ethereum itself is more decentralized than all traditional value-transfer networks of the old centralized financial world, and the applications built on top of Ethereum are also a spectrum of decentralization.
But how do you measure it? What is the degree of centralisation of the "traditional value-transfer networks of the old centralized financial world" (your words)? You said it was greater than that of the ethereum network so you must have measured both.
They were not my words, I was merely inserting a lame joke.
As far as I know, there's no technical metric to measure decentralization, instead it's something to reason about, as it can touch many aspects.
However, if you insist on finding a key aspect that indicates how centralized or decentralized a protocol is, the answer typically lies in nodes. How many are there and more importantly, how accessible is it to run your own?
With Bitcoin, anybody can run their own node, even on modest hardware.
With Ethereum, considering the future PoS switch, only rich people can run a node, unless you join a pool. The minimum ETH required is 32 ETH, which make it an elite thing. Worse, those elites will get even more ETH as a reward. This doesn't necessarily mean ethereum is not decentralized at all, just less so compared to Bitcoin.
A worst example may be ICP (Internet Computer) where running your own node is close to impossible.
Ethereum itself is more decentralized than all traditional value-transfer networks of the old centralized financial world, and the applications built on top of Ethereum are also a spectrum of decentralization.