I don't know what magical super resolution you play at, but I can read the font size in Steam just fine. I've never heard of anyone else having a problem with it either, but if they do, their eyesight is probably so bad they need to use a 400% zoom on Firefox, or more likely, they just lower the resolution because their eyes don't work. Regardless, I fail to see how the company that does accommodate things like colour blindness and deafness is so out of touch for not including the ability to change font size. They're certainly not as "face palmingly stupid" as everyone else in the industry when I can name maybe half a dozen games that accommodate colour blindness and none that include variable font size.
The majority of users don't have multiple hard drives. The ones that do are probably smart enough to figure out how to run Steam on their program drive and the games from another drive. It's actually pretty simple.It's out of touch, just like how they don't support multiple hard drives, when the current trend for the past few years is to put in a larger general hard drive and a smaller solid state one. Many gaming rigs actually utilize multiple solid state drives and run into the same problem.
The lag in voice chat, anytime I've used it, isn't exactly a huge problem. It's small and really the voice chat in Steam is just a tool of convenience, it's not meant to be some hyper efficient Skype competitor.Then there's the lag on the voice chat. The in-game interface not compatible with every game automatically. Cloud save issues. Download slowdowns. I could make a longer list, I just thought it would be redundant.
As for the in game interface, I assume you mean the Steam overlay when you shift+tab in game? I've never seen a game it didn't work with aside from Morrowind which it can crash. I'm inclined to give it a pass for that since Morrowind is a year older than Steam, and, you know, it's Morrowind. It'll crash if you look at it funny or failed to properly drain the goat of all of its blood when you sacrificed it to Bethesda.
Cloud save issues and download slowdowns I'd be somewhat curious to hear more about. I've rarely used cloud saves, but have never had any troubles with syncing or getting the most recent save on the rare occasion I did have to use it. Download slowdowns happen, but usually I'm getting a solid 2Mbps when I download and I frankly have problems with my ISP more often than Steams servers these days. I honestly can't remember how many years it's been since I had relatively frequent problems with the Steam servers. I know some people still have issues sometimes, but it's the nature of the beast when you're dealing with dozens of different hardware configurations, untold thousands of potential software conflicts, and your average user being dumber than a sack of hammers.
No honestly, I'm not saying Valve is perfect. Far from it. But I could rattle off a better list of actual things they kind of cocked up in the last few years than these. You honestly seem to be either reaching, or you've got some odd priorities when it comes to game distribution software. But for all of the faults that Valve does actually have sometimes, like some pretty bad cases of troutty programming for starters, they are at least constantly trying to improve everything, and implementing a lot of features that the other big name platform owners are years behind in even attempting. In fact, I'm usually willing to cut Valve a bit more slack than I would your Microsoft's, Sony's, and Nintendo's if only because when they screw up, it's often because they're doing something totally new and trying to stay ahead of the curve (Steam workshop, Greenlight). When the other guys screw up, it's usually because they're adding features no one wants, new UI's that are objectively worse than the old one, actively removing features people paid money for, or just making a bad firmware update that has as much chance of bricking your console as working.