whatever is going on with you is not the case for me. i'm getting off rule sets 90% of the time even if i get placed in a 1v1. what i do know is that if i change my preferred rules to casual settings, i am guaranteed that, but there is so few people looking for competitive match ups that the matchmaking decides f*** it and puts me in these lousy four player matches i don't want to be in.
people all the time tell me to "Git Gud, and raise your GSP to find better matchups." but not only is my training strictly based on competitive rule sets, these free for alls nearly always end the same way. i go on the offensive, and i get punished for doing so even if it was only for a split second. if i don't die as a result, i usually take an average of 50% damage because the mayhem of two people fighting locks off a bunch of landing options leaving the third player to have a field day with me as their sandbag. don't even get me started with the 3v1 matches i have had forced down my throat.
i'm even more helpless against anyone in a free for all. it also doesn't help that some of the items open up the possibility of death at 80% or even less sometimes, and certain stages with hazards on are no different than items. air dodging was nerfed to the ground by the way, so that adds to the problem as well. and to top it all off, my solo main, ness, is horrible at crowd control compared to hard hitting tanks like king k rool and ganondorf which really hurts my chances. the gsp system will not allow me to progress through it in battles that truly test your skill.
i can't progress through an army of free for all battles with items on. it's just not going to work in a million years. getting better at the game really wouldn't help me raise my gsp.
the thing about arenas is that it's extra hard to find someone of the same skill level. it's suffering the same issue as sm4sh's for glory option. with no system in place, everyone i meet either obliterates me, or i obliterate them, and the match ups are never fun even if the competitive rule sets are there consistently. arenas are often not fun to play in.
It's really odd that you're getting 90% of the rulesets being off of what you want. I take that figure literally, of course. Technically, you should be getting your ruleset 50% of the time at all times, at least that's how the ruleset system appears to function. Here's something you can try:
1) If you did a digital download, try reinstalling the game entirely. Maybe something broke during the install/update process that didn't break things enough to prevent the game from loading.
2) Make another Switch profile and test rulesets/online with it to rule out your save as an issue (not 100% if it works like this).
As for training, take it offline for a bit. There are a ton of fundamental things you can practice offline, like spacing, zone control, reactionary options selection (not option selects), movement, etc. Believe me when I say that fundamentals can carry people a long way. Beat on a Level 1-7, form gameplans, and get really, really comfortable with Ness. After that, return Online and things will seem so much easier. I can promise you that one.
For FFA, I don't play Ness so I don't have specifics. To win FFAs in general, though, stay just barely within the fray. Not too far in, but far enough out to react to someone's approach and make it look like you're doing something and in the FFA. This completely removes focus from you in 2v1 and 3v1 situations. Run away as needed, but return ASAP. Soon you'll be the one on the 3 side of 3v1s. After that, it's easy to come in at least 2nd in a FFA, which is always a GSP gain. Not as fast as first place, but all increases are good for our purposes here.
And, considering you're forced into an FFA, all tactics are fair game. No matter how lame.
For items, play some CPU matches with all items on high, and focus on them. Get a feel of them. In your competitive life, the use is limited. It still helps to learn, though. Lets you deal with FFAs even more AND it helps in some Matchups, like Pac-Man, ROB, Peach/Daisy, etc. There is a lot of fun in Z-drop shenanigans, so it's not like dedicating time to the items in general is useless. It'll help.
Forget about what I said here, online is a mess and need to get fixed, if you want more detail of the reason why am I saying that I made a post here: 