Races in DCSS are essentially difficulty settings (they’re labeled “Simple”, “Intermediate”, and “Advanced” in the menu); most good players don’t play MiBe over and over because they’re fairly easy once you understand the game and there are more interesting and more challenging races to play once you’ve mastered the basics. (Also I don’t think they’re nearly as trivial as you make them out to be; I just queried my games and I’ve only won 50% of them online, and I’ve certainly killed many more offline when I was learning the game.)
The tournament I’m in currently forces each player to play a randomly selected race & background combination each week. You only get one shot each week (well technically two if you die before XL 5). You get points for completing certain milestones, worshiping certain gods, and each week has unique challenges that get you additional bonus points. I think it’s a fun way to play DCSS that forces you to learn a bunch of different strategies and playstyles, and play in a careful and conservative manner since you only have one try.
I do think Brogue is much better in terms of mechanical transparency and simplicity, but DCSS does try to surface a lot of information in the game and has been getting simpler over the years (a main complaint from older players that have fallen off is that the devs remove and simplify too much). The design goals explicitly call for skill based gameplay, meaningful decisions, avoidance of grinding, and playability without need for spoilers. You can certainly argue that they don’t achieve all those goals perfectly, but it’s closer than a lot of other games I play. I don’t think any of the devs would say it’s a perfect game, but they’ve fixed a lot of the low hanging fruit and most of what’s left are hard problems without obvious solutions.
You mentioned the ‘o’ key, which I think is a good example of a hard problem. If a character is doing particularly well some parts of the game could be boring, so the ‘o’ key is an attempt to automate exploration to reduce the number of trivial decisions the player has to make. Ideally the ‘o’ key reduces the time between interesting situations, so that the player has to make meaningful choices more frequently.
Certainly there could be other solutions to this problem: they could make floors smaller to reduce the tedium, but then that affects the player’s ability to run away or avoid threats. They’d also need to increase the experience every monster gives, re-balance how many enemies spawn per floor, potentially resize all the handmade vaults, maybe change spell ranges, how far sound travels (you wouldn’t want to wake every monster onthe whole floor since it’s smaller) and it’s not entirely clear that a better game would come out the other end. A lot of mechanics that currently result in interesting situations would have to change and be re-balanced to support that.
Maybe it’s a shitty stop-gap solution, but I don’t think it’s designed to be compulsive. I think the same game without the ‘o’ key is certainly a worse game because you’re spending more time in the boring parts.
As for randomization: I think it’s largely to force the player into new situations they haven’t been in before. Good players can win many games in a row, so I don’t really think it can be a gambling compulsion at a high level. You could argue worse players might get some gambling thrill out of it, but since ultimately player skill has a much larger effect on winning than getting good gear, their time would be better spent trying to learn the game, rather than mindlessly mashing and trying to get lucky.