What if they released the exact same product as "minimize fuel cost if it doesn't take more time" and set that to default? You can still change to "fastest" if that's your preference.

My personal annoyance: their walking directions assume you don't know parkour and there isn't even an option for that

I genuinely cannot tell if that last bit is sarcasm or not!

It's a near-truth, told to own my selfish tendencies while I'm on the topic of somebody else's. The truth being that I don't want that info from google, rather I delight in beating its time. I do wish that I could dial in a walking speed, though, and so do people with reduced mobility.

If you read the article, there's an option in the settings to not have this option "forced" on you. Even when it's "forced", it's only defaulting to more carbon-positive routes when the ETAs are comparable, so it shouldn't have much of an effect on whether you care about the feature or not.