tldr: longer reorgs and less energy mean less security. Which, is presumably the reason to even use a blockchain
> Okay, fine, under normal conditions bitcoin blocks are 98% likely to be final but ethereum blocks are 80% likely to be final. However, six bitcoin blocks provide a one minus one in a billion finality guarantee (since 0.02 6 < 10-9) and 13 ethereum blocks provide that same guarantee (0.2 13 < 10-9), so it's still the case that what bitcoin provides in 60 minutes, ethereum provides in 156 seconds. Sure, not in six blocks, but it's a battle of linear versus exponential, so the more fine-grained you can make the single-block confirmation time the better.
There are also uncle rewards which mitigate the miner incentives.
I see benefits to both systems and longer block times are clearly more efficient, but since Ethereum is an application platform a 10 minute block time is untenable. It may be less efficient, but I don't think thats a nail in the coffin.
Another important thing to remember is that Bitcoin has a block time of 10 minutes. That means that once your user submits data to the blockchain, they need to wait ~5 minutes for even 1 confirmation.
Ethereum has a block time of 12 seconds.