RNG in a competitive title is not inherently bad design. As long as all variations are rewarding for the user while also providing reasonable counterplay to the opponent, it is an acceptable element of the game. I have no idea why the concept of RNG gets so much hate around here but it's gotten rather silly.
I don't know how I feel about the specific examples you listed, but I'd like to back you up on this premise and offer my take on the subject.
Randomness works just fine in a competitive game where it is capable of testing the skill I call "reacting to unpredictable events." How can this skill be tested in a way that doesn't effectively end in raw gambling?
One, the random factor cannot be unreactable. This is the primary reason items got turned off back when Melee was young: that game has no way of turning off item containers, which have a 1/8 chance of exploding, so all items had to be turned off lest they dropped in front of your smash attack and killed you. Peach's turnips, for example, are a little better about this, other than that it can be hard to tell if she pulled a stitchface or not (PMDT, red stitchface when?); her turnip pull animation is pretty long, so you're paying attention to what she pulls, and if she pulls an item there's a different audio cue.
Two, the results of the random factor cannot be overbearing. Losing the random outcome has to be a little worse than winning it for this to be meaningful, but the difference can't be so stark that the random factor decides many games. As completely unnecessary as tripping in Brawl was--it was a flat out bad mechanic, nobody here's gonna argue with that--tripping actually very rarely decided the outcomes of Brawl games, which is why it wasn't what killed Brawl despite being universally maligned (the pacing and character balance issues were much bigger factors, but that's another discussion). Random stage selection, however, could very easily decide sets--before everyone moved to stage striking for game 1, many old Melee rulesets used a random stage game 1, and if you know the difference between Marth on Dreamland and Marth everywhere else, you can tell why we no longer do that.
tl;dr: Randomness has to be something you can reasonably react to and cannot be so influential as to be the deciding factor in games. Once those two factors are fulfilled, randomness becomes arguably helpful, since it shuffles situations around enough that players can't just preplan everything, but instead must be ready for many scenarios.
Also, "randomness" after a fashion is inherent in competitive smash due to the little necessity we like to call seeding, but that's another discussion.