Linux is of course very impressive and most Ethereum nodes run on Linux. But you can peg a machine to a specific version of Linux and never have to upgrade if you desire. Your machine is ultimately independent of other Linux machines. The key challenge with a blockchain is that you have to keep what amounts to a globally distributed and permissionless data center in sync with protocol upgrades and the cost of making a critical mistake can be in the billions of dollars. You have to account for not just technical vulnerabilities but game theory vulnerabilities.

The challenges are of course, entirely different in OS kernel land. All of them are impressive.

I'm fully aware of Linux... It's also a very impressive open-source project. To elaborate, reason I consider Ethereum to be more impressive is the collaboration between maintainers and releases of different clients and client versions in different languages. This happens with different packages in Linux to some degree but on Ethereum it's a different ballgame because it's a live system, it's not like you can just let some users upgrade to beta versions and fix bugs as you go, everything has to work together perfectly with a system-wide change happening in under 12 seconds globally with billions of dollars on the line. There are testnets but no true analogue for mainnet. (Edit: chrisco255 below said it better)

Seriously... Too many people just buy the excuses of these systems even though there are massively distributed systems that work on existing technology quite well. Crypto is just an excuse to scam others with the promise of $$ rewards using words they don't understand and seeming to be high tech.