There are a lot of players out there like this. You can beat some pretty skilled players but have issues with super basic, beginner strategies. You think they shouldn't work on you, but they do, and you don't know why. It's because you're accustomed to playing against good people, that you're looking for common habits that newbies and non-competitive players don't express. Good players don't sit and spam Mii Gunner's fsmash or missles. You can probably destroy a beginner competitive player, who's trying out actual competitive strategies, more than you can beat people who have no competitive experience and just do what works? Because that was me in a nutshell for a long time. I always felt that because I was "playing correctly" that I should get wins. I was super wrong. I dunno how many For Glory Samus players I lost to at the beginning of Smash 4 who just rolled to each ledge and spammed missiles and charge shot because I was trying to go for reads and cool tech and got hit by their crap. I was more concerned with how I wanted to play the game over playing the game that was presented to me to get the win. Back in the Brawl days, I watched pro videos and tried to copy them, but didn't always know why they were doing what they were doing. I just knew it worked on other pro players, so it would probably work for me. It was kind of like trying to build a house out of toothpicks and Elmer's glue over brick and mortar. It stood up until someone gave it a good kick, then it just fell apart entirely.
Don't try to outsmart them, but you can probably out-dumb them. Anything you would normally perceive as a bad move against competitive players, put it on the table as an option versus these guys. These people don't play neutral, they have no concept of it. Every move is basically as if they are in advantage or disadvantage, and nothing in between. I'm sure you've ran into the Link players who camp the ledge and play like a flowchart...Throw boomerang, shoot arrow, throw boomerang, shoot arrow, run in and dash attack when you try to jump over it to approach. That's the one thing they know, so you can generally get away with playing like an idiot otherwise. The thing that used to really bug me was the scrubby roll-behind crossup. Doing it made me feel like I was a bad player, so I never did it. I was always told you are better off shielding or rolling away if you need to roll at all. You never saw good players do this because it was generally a bad option against other good players. But...players with spammy and annoying strategies may not know how to deal with it. Or if they're spamming projectiles, just shield and spam projectiles back at them. PK Freeze them until they quit it. Absorb what you can and get free health back. Or reflect them until they actually decide to approach within your range, Lucas's fsmash reflects stuff. I've had people ragequit on me because I learned how to beat their main gimmick that nets them online wins and they don't know what else to do.
Heavies can be scary if they're good players. You have to be super careful with your spacing and move in to punish when they whiff their laggy stuff. Almost all superheavies in this game are susceptible to a good projectile game, and most of them have a really exploitable recovery that can be spiked. But if you're talking the DK players who just, like, do dash attacks all the time, you just need to jump over them and hit when they're in endlag. Those types of DKs are all over the place online. Just don't be afraid to use all of your ranged options.
There's a term for someone going into a game with zero prior knowledge about the game or how it works and being successful, just by doing what works over what they want to do. They have no habits at all, so they have no bad habits you can exploit. I honestly can't remember the term, but this may not always be the case, but it can be the case here and there.
I guess in short, don't fall prey to their trolly dumb stuff. Adapt to it as the game goes on, and counter their dumb stuff with your intentionally-dumb stuff while not forgetting your smart stuff like good shielding and edgeguarding. Also, maybe avoid quickplay if you don't want to deal with people not rematching. Join or make an arena and continue to play there.
