Yes. Bitcoin can be validated with with regular hardware, thus full nodes are cheap and ubiquitous and results in a system that's highly decentralized. Even if a 51% were to hypothetically happen with miners, the full nodes will stop it.
Ethereum and many others with massive blocks cannot be validated with regular hardware as there's too much computational power/storage involved. The majority of Ethereum nodes are by 3rd party services which use cloud services such as AWS. Additionally, essential services such as Infura which the majority of apps rely on are basically entirely centralized.
You can sync a full ethereum node (all blocks with all transactions and fully verified current state) on a rasberry pi with a 1TB ssd. With 3TB of ssd space, you can even have an archival node (the above, but with all the state history changes cleanly indexed by account, which is only really needed if you want to run a block explorer).
The issue for ethereum flat out isn't the hardware requirements, its laziness. Infura, Alchemy, et al make a very convenient shortcut for impatient folks and that is why they get used. The good news is that there is a ton of real development going into light clients that can trustlessly get and interact with with the current state of the chain within a few minutes of launching and can even run within a web browser.
Exactly. If validating the ledger requires millions of dollars worth of hardware, only a few people will know what it actually says, and they can collude to impose whatever rules they want (basically like what happened in the article).
is it that specialized equipment is not easily accessible and thus not truly decentralized?