Things in RPGs that you used to like but don’t anymore

[False God]

I don't think that's an accurate assessment of how a d20 RNG works. At the extreme end, a d20 allows more consistent results than dicepools (though equivalent to something like 2d10). If you have a +10 bonus on a d20 roll, you will succeed on a DC 10 check 100% of the time (barring epicycles like nat-1 auto-fails). Conversely, if you roll a dicepool of five six-sided dice that hit on 4+, you will fail at a task requiring one hit a bit under 5% of the time (again, barring some epicycle like allowing people to default). Flat RNGs simply do different things than dicepools, and are suited to different sorts of games. In a game where hard-core badasses can expect to take on armies of normals, a flat RNG is better because you can push people off the RNG without needing any extra mechanical work. In a game where "the cops showed up" is supposed to be a lose condition for even high-power characters, a dicepool is better because it limits how powerful characters can be.

A "1" on a d20 is a 5% chance.

But your logic follows my general movement in gaming, as I've grown less fond of games in general where "the cops showing up" don't mean anything. Even in D&D, the "cops" or town guard or whatever, very quickly become meaningless threats, and it shows with how prevalent murderhoboing is in the system. In systems where "the cops" (average joes with average weapons and armor) are a very real and present danger outside of the most insane of characters, I find players behave less like gamblers and more like rational people.

Not liking the d20 and its wonky flatness is why several systems have been 3d6 for a long time (GURPS and HERO having been around for decades now). And yeah, die pool mechanics largely don't address the issue.

What's funny about this thread for me is that I have to go back decades in some cases to find when things that bother me now related to RPGs... didn't bother me at all or at least not nearly so much.

I get the feeling that there's a happy medium in dice-pool systems somewhere between 3 and 6 dice. I've generally found that large dice pools don't really produce that much more success. Sure, 5/15 successes can really wallop an enemy, but it's still statistically about the same as 2-3/5 successes. Some kind of reduction in the number you need for every 5 dice you'd have beyond 5, I dunno or something, I dunno. More dice, like higher modifiers, should mean more success, but it really doesn't.

And I find 7+ dX to be kinda wonky to hold anyway.

One advantage d20 (and linear RNGs in general, especially d100) has is that it's dead easy to calculate success probabilities. What's the highest number you fail on? Multiply that by 5 and that's your probability of failure. There's no similarly-easy trick for 2d10 or 3d6, though they're not too bad to do offhand. Dicepools are easy to calculate average successes for, but figuring out the probability of "x or more hits" for non-trivial x is something very few people even know how to do without looking it up. I don't even remember what the formula for expected value on roll-and-keep is.

As above, for the people who understand this math, and I mean REALLY understand it, unless there is a flat 0% chance of success or failure (depending on the case) it leads to poor decision-making via gambling. When a d20 has a 5% chance to roll a 1 and a 5% chance to roll a 20, even if your only chance of success/failure is on one of those numbers, I find people more likely to gamble at "winning big" rather than take approaches that may lessen the difficulty but consume resrouces.

As I mentioned before, when I tested out 2d10, it was a much smoother game, with far more successes for the players, but far fewer "OMG A NAT 1 I'M SO DEAD!!!" and far less "OMG A NAT 20 I WIN OMG OMG OMG!!!!" Which is an unhealthy (IMO) gamblers mentality.

Not to say risks shouldn't be taken, but if you're always gambling on the "big wins", the game itsself becomes background noise to the extremes.