A number of suggestions:
1) Sounds like all you do is look for tactics. You need to study concepts in positional play. Do you know what a "hole" is? How about a "backwards pawn"? Could you identify the "Worst placed piece" in a position (I bet not, worst placed could be a piece well into your opponent's camp)? Do you ever give up a Rook for a Knight or Bishop when not "forced" to do so without there being mate or an immediate way to get the material back? Do you know WHEN to make such a sacrifice?
2) Minimize blitz to only being played when you have a few minutes to kill. If you are playing more then 2 or 3 games at a time, you are playing too much blitz. Time is better spent studying.
3) Do you play over the board in tournaments at all? Or rated long time control games at a club? If not, highly suggest you start.
4) When you study, are you using a board and pieces? Or are you only looking at UTube Videos and PGN Files? Visualizing on a 3-D board makes a big difference. Get out the board and pieces, book in hand, and study the old fashion way. It really works!
So way back when I used to have a very rote repetoir. I used to play as white the Scotch (for whatever reason), the c3 Sicilian, or respond accordingly to something unusual. As black I'd play some strange Sicilian lines or maybe the Nimzo-indian. Bottom line was I didn't play much else unless I was really bored.
And it seemed to work to some degree. I did pretty well in bullet and blitz. Playing somewhat consistantly around the 1450-1550 level. But this was years ago. Recently I've started playing everything and anything. I've payed a ton of lines across any number of openings. I now play najdorfs, frenchs, ruy lopezs, the grob (idk why), QG lines, some strange queen-pawn stuff, caro-kann, the English (though I know 0 theory), and much, much more.
Bottom line is I spend much time studying openings, but improvements are few and I've kind of plateaued much below what I used to play for Blitz/bullet. I can beat people 1500-1650 every now and then, but I can't seem to hold any consistant record against lower rated players.
My tactic trainer rating is super high, so I doubt I'm failing too much from tactical play in the middle game, and endgames seem to be a persnal joy of mine, so where am I going wrong? I can't seem to figure it out, and I think I really would like to be playing at a higher level. I suspect my openings might be to blame.
Any pointers?