Re: the questions;
I've always fantasized about designing a system that has no randomness at all, but never gotten too far. I think the issue comes down to the fact that a game where every outcome is guaranteed is a very different beast than one with chance. While discussing this very thing with one one of my friends, she referred to such a game as "basically a very complicated chess match" and while I don't mean it as derogatorily as she did, I think she's basically right - such a game seems to me to quickly become one of trying to predict all your enemy's possible actions, and how you'd respond to them, in a way that other TTRPGs, even very tactical ones, don't. A possible solution would be to obscure the enemy's possible actions - perhaps combat could be a game of experimentation, probing the enemy for weaknesses while adapting to the abilities they do have! It would be quite difficult, I think, to design enemies that feel fair in such a system though.
Regarding the spectrum of certainty and chaos, though some amount of chaos can occasionally be fun I tend to prefer games with more certainty. I'm very fond of games that rely on manipulating RNG, effectively controlling the chaos. Pathfinder second edition is an excellent example of this, much of the combat loop is about gaining bonuses and inflicting maluses to make your attacks more accurate and more likely to crit. But, in truth, I do not feel they go far enough. Let us take a momentary step outside the genre, and consider the videogame XCOM2. Now, if you're familiar with the game only from internet memes, you probably think it is a game that leans much towards chaos (as, in truth, it's predecessors in the series did) however! XCOM2 plaid well is much more certain - it's much less gambling and much less counting cards.
Like pathfinder, one of the core systems of the game is gaining bonuses and inflicting maluses to gain accuracy (the other, by the way, is target prioritization - a very fun facit of the game, though already a TTRPG classic) however unlike Pathfinder, XCOM both allows and encourages you to go all the way, combining positioning and buffs such that your shots have a 100% chance to hit. It is effectively a game of forging certainty out of chaos, and I adore it for it (and many of the game mechanics really encourage you to go for 100%. For instance, some enemies have a "dodge" chance separate from accuracy that's simply a % chance to take half damage from all attacks - all attacks except ones with 100% hit chance. It's no surprise that the best trait of the game's grenades is not their area of effect or even their ability to destroy cover, it's simply the fact that they never miss.)
I think that a similar system could easily be used in a TTRPG to magnificent effect. I imagine a three-player excitedly strategizing how to synergize their abilities such that a previously untouchable boss could be hit certainty. Of course, such a system would require some substantial changes from XCOM, for instance XCOM's heavily covered based gameplay would likely not suit a TTRPG well (I've never played a TTRPG where cover felt good - though perhaps that's merely my lack of experience!) especially if it was being adapted to a setting that commonly features melee weapons, however none the less I think it's key principles would make for an excellent TTRPG experience.