Not all game devs can even REACH that threshold you're talking about, so it doesn't mean much. At best it is major publishers like Capcom, MS, etc. along with popular indie devs (creators of Hades, creators of Don't starve, as an example) that can reach that milestone and from afterwards get a smaller cut on purchase of their game on steam. Smaller and medium sized indies couldn't reach that milestone on steam for years.
Furthermore this milestone, it would be for total revenue/sales on STEAM, why would valve consider the revenue the dev or pub earned from purchasing or redeeming a key?
This argument that a lower cut for major successes is bad and the little guys should get the lower cut instead doesn't solve the issue for failing projects AT ALL.
First of all: Someone that needs 5 or 10% more to survive is quite rare in the first place. Either you are profitable with a 30% cut or your game tanks and those 5 to 10% wouldn't help you anyway.
Second: Learn to budget correctly! 30% is a known "expense"! Sure, you can't really know beforehand if your game is a hit or not, but you can budget your project that it will have a certain range that it would realistically and historically sell (if you have existing games/series or experience making games) or this is your first project and there was no guarantee that it will make money at all.
Third: WHO IN THE HELL is budgeting their games so precisely that they would be bankrupt at 30% and profitable at 20%??? And if you know that in the first place, then cut the expenses beforehand, because you know that you have a 30% commission!
Fourth: Even if the Industry standard gets down to 20% Most bigger companies will just pocket the difference and smaller devs and indies will just pump more money into the game because they think they have 10% more cash after selling the game. Now we have the situation that 20% is too much.
Sorry if this comes across a little aggressive, but the little guys versus the big guys narrative is bullshit. Several AAA Studios don't get 20% while small indies get it (Valhalla and Among us just recently)
Not size matters, but success.