IMHO this whole situation exists in the first place because of Steam Direct. And Steam Direct exists because Valve couldn't keep up with Steam Greenlight. And Steam Greenlight existed because Valve got sent some indie games like Minecraft - I'm not sure if they actually saw Minecraft, I think so but I'm not sure - and decided against selling them, and then when they came around a lot of sales were lost - and in case of Minecraft Mojang decided to avoid the cut since the infrastructure was ready.
The Steam Direct setup means that there are lots of indies who try and lose. You will see some people complain about it, but most are probably understanding that their stuff just didn't take off. The developers which complain the most are the ones who would have been on Steam under the semi-manual checkup, because they know people would spend more time with their games wasn't it for all the other stuff, good or bad.
Based on this diagnosis, Valve can do various things. One thing they were planning to do was releasing Source 2 under no cut as long as the games come to Steam. This was a very good idea in theory, the problem is that Source 2 is vaporware. If Valve is willing to do moneyhats, the greatest target would be Unity Technologies, proceeded by the exact same deal involving Unity. Alternatively they could actually go and make that Source 2 work, and be greater than Unity and Unreal, and that would be helpful, but not quite there, I think it would be way easier to buy out something essential.
An alternative is to attack the "problem" itself by essentially desyncing Steam Store into Steam Delicatessen and Steam Warehouse. This cannot be a hidden data recommendation thing or else people are not going to believe it, these must be two separate, visually distinct sections of the store. Steam Warehouse would be where the games go by default, Steam Delicatessen would be were users go by default (with a big button allowing people to go to the Warehouse). Direct would allow the game to enter the Warehouse, Delicatessen would involve more madness, but it would have to be formalized madness, possibly with multiple paths. The thing left to figure out is how the hell do you convince people to check out the Warehouse, but I'm pretty sure Valve could figure it out once it would be a formal thing, instead of just some games appearing on front page but not others.