“are the devs happy with it? Is that the standard for digital stores as well?”. And the answer to both is Yes

I fully disagree. On the first point, do developers accept it? Sure. That does not at all mean they are happy about it. Money is tight for games, and I guarantee you every developer would much prefer to take a bigger piece of the pie.

To your second point, it is the standard but it is not universal. Epic Games Store takes 12%. Itch.io defaults to 10%. Google Play Store takes 15% on the first $1 million in revenue.

But that alone doesn’t impact me, the consumer.

I don't believe this is entirely true. The more cash flow developers have, the more stable they are as companies, and the more able they are to put out good games. You are indirectly impacted because a larger tax on developers means fewer, or lower quality, games that get released.

Steams share has zero impact on my wallet.

~~Disagree, unless you exclusively play AAA.~~

Edit: Actually I've changed my mind on this. I mostly agree the percentage cut doesn't affect the optimal price point.