30% as industry standard
That's the same as app stores/etc, and is still a common cut to take. I'm not convinced the cuts that Epic is taking are actually sustainable for offering downloads/updates/etc for a game indefinitely, but it's hard to tell since the Epic store is already bleeding money.
I'll also mention that Audible (which has a monopoly in the audiobook space) reportably takes a 60-75% cut of audiobooks sold on their platform (they take only 60% if you agree to sell exclusively on audible, but they take the full 75% if you want to sell the book somewhere else as well). Monopolies abusing their position is really common, but I haven't seen anything similar from Steam that makes me think they're abusing their position. I suspect PC gaming would be in a far worse state if another company controlled the popular storefront.
Repair electricians definitely run into the work of install electricians, but my experience is they're mostly two different groups. Install electricians may come back to do repairs on their own work, or if there's a lull in new construction jobs they can pick up they might fill in the hours with some smaller repair jobs.
There are some some more specialized electricians that do a mix of both, for example my company is mostly generator focused. We're involved in both new construction and repairs for things that are generator/transfer switch/solar related.