So yeah, probably Lichess is the better option for me. For some reason, my rating there is 1930 and on Chess.com I am now rated under 1500. I would say that was embarrassing, but a lot of the time I am being beaten by guys with a 90-98% accuracy, having spent about 3 seconds on each move, so I just laugh after some games.
On lichess you start at 1500 instead of 400, 800, 1200, 1600 or 2000
Anyway, it looks like people will argue about this all day, I have said my opinion, that is all.
You are close to 1 900 in rapid. People at that level will know a bit about openings.
Now I think that you are exaggerating when you mention 25 moves of opening theory. I am looking at your games and you've won many games where opponent has less than 60 accuracy and so on. So that is certainly not a GM level of play.
As for let's call it "fishy" play in online chess... I am playing long games pretty much exclusively (45|45 and 60|0 most of the time). People believe that in such games they will encounter fishy play in every game, and the truth is that I rarely encounter such opponents (perhaps every 20, 30 games someone is banned). I generally rarely feel that I am playing against someone who is not playing fairly. Many people avoid long games because they fear they will be cheated, and the irony lies in the fact that it is most likely a bigger problem on higher levels in blitz games.
Because of this fear, people around 1 600 rapid rating are the highest rated people (apart form a few exceptions) who plays 45|45 and 1 hour per side. As a result, I mostly play in a smaller pool, and people like me may have unreliable ratings. We can either be accurately rated, overrated or somewhat underrated.
I am sure you will encounter fishy play as well, probably in a slightly bigger amount compared to me, but I wouldn't worry too much about it. There are people who cheat on every site, and you should just report it. I believe their detection level is pretty good. In fact, I think there were never a case where I was sure 100% that the opponent is cheating and that opponent wasn't caught soon enough.
As for gambits, I never play them for instance. I feel there are just better openings at my disposal so I never bothered. I mean there are some sound ones (Smith Morra is fine and I encounter it from time to time), Benko is a legit opening as far as I know, but I am not 1.d4 player, but there are too many bad gambits, and those are rarely played in longer games I play. It is understandable that most people your level will rarely play unsound gambit lines. They wish to defeat you after all. Of course, in blitz chess, it is more logical to play gambits from time to time, I mean you might flag your opponent as well...
You can switch to other site, and you will encounter gambits, but when you get your rating to comparable value (roughly + 200-300 points compared to here), you will probably not feel a difference.
If you really wish to experience playing weaker people, you can always play 1 or 2 unrated games against slightly weaker people. As for your rating which is not what it used to be, that is normal as well. A lot of people has seen their rating diminished since Covid and Queens gambit series. So many people have created an account and there are many people who had their highest ratings a few years ago and now their ratings are 200 points weaker.
I have started playing myself last february (I did play when I was a kid, but haven't played for 20+ years), and there were many games where I defeated players that were let's say 1 600 or 1 700 a few years ago and now they are 1 400. And their level of play is just not up to standard for someone who is 1 700 today.
Sorry for the long post, I just wanted to address many things you've mentioned.