Yeah, that's the problem. High level opponents know how to play as themselves and then change it drastically. So devoting anything but primarily full attention to their habits can really get you put behind. If I could make a recommendation for getting a feel for your opponent, do a few standard things like throw fireball, come in with an aerial, move towards them in a definitive way, and look really closely as to how they react. You'll spend a while seemingly not accomplishing anything, but after you've got a feel for them you can get into the match with your understanding of their habits. The technique is called "feeling them out" and is used a lot more in other games, but not as much in smash.
Another part of reading your opponent is assuming a few things, like players natural inclination to tech away when given the opportunity to tech, or that most players will try to shield grab aerials, and then spending the early part of the match teaching them to not do those things. Then all your mixups are fair game, you get a good lead doing those things until they break the habit, and in really clutch moments you know what they default to.
And bad habits are the crux of looking for players habits. If they've got one really bad thing that they do when put in a certain situation, push them to it. The worst habits are the hardest for the opponent to break as they're only their because of some deep seeded inclination to react in a poor way.
Edit: also a thing I noticed in your matches that could really help you out is that you'll use Dair and land behind the opponent and go for jab, or Utilt, or Dtilt, or some other combo starter, and if it doesn't combo off of Dair the opponent just shields it. If you started going for grabs after those cross up Dairs you could really threaten your opponent, as staying in shield gets them grabbed and trying to SH an aerial gets them Utilted. Spot dodging doesn't matter because they still have their back to you, and you can chase rolls to grab.