Ethereum is not Bitcoin because Ethereum doesn't want to be Bitcoin, otherwise Ethereum wouldn't have existed in the first place. That's like complaining that GCP is not following the advice of AWS "leaders", of course they are not gonna do that, otherwise they would work together, not on two different projects...
Also, no matter what Satoshi wrote in 2010, multiple implementations of Bitcoin does exist today, most of them relatively stable: https://en.bitcoin.it/wiki/Clients
And the integrity of the network is not harmed by multiple clients either, just harms the users of that client, not other clients so not sure what the harm is. Yes, it's difficult, but so is a lot of problems in the cryptocurrency space.