That is were I think Hemlock and CapnZapp can help you. I'm pretty sure you can optimize / power game to minimize the "arbitrary randomness of 5E's overwhelming focus on die rolls,.." At least that is what I have seen from their examples in the past.
Also, since I am not familiar, how do other games reduce the randomness of die rolls? Do you want to use die polls? Obviously advantage provides this to an extent, but that is not really a thing in D&D.
Yeah, 5E combat essentially isn't random at all. Good play utterly swamps die roll randomness, at least within non-uberdeadly combats. The most important thing you can do is first gain an advantageous position; after that the die rolls are just details.
Generally, if you want to minimize the effects of random chance, you need to increase the number of die rolls involved. (Law of Large Numbers.) If an entire adventure hangs on a single DC 20 skill check that can only be made once, then that adventure is going to be swingy and won't feel like it has much agency. If the skill check just controls whether you go in the front door or the back door, or if you can make separate checks for each door and either works, it will feel less swingy. Similarly, if you need to succeed on 8/10 DC 15 skill checks, and those skill checks are affected by situational modifiers (from player choices), then even though some randomness exists, it will feel like there is a high degree of player agency and a low degree of randomness, because that's just how probability works.
One reason 5E combat isn't very as random-feeling as skill checks is because there are so many rolls that results come out close to the expected values.
I didn't read Curse of Strahd very closely but I don't recall it being written with this insight in mind. I'm not particularly surprised to hear that it feels swingy for the DM; I expect that you'd need to rewrite it slightly, using a good understanding of probability, to get it to feel less random. Add multiple paths to success, and add multiple gates to success along each path, etc.
On the other hand, if the
combats are feeling swingy, then the players just aren't playing efficiently. Which might be just fine with them BTW. Not everyone likes to think in terms of decision matrixes and probability densities--some people really
do enjoy playing Chutes and Ladders, where the biggest excitement is seeing what numbers come up on your dice this turn.
-Max