I’m no expert, I’m only 500 hours into my aim training journey, but I see no one has answered so I’ll give my takes.
1: I had around 2500 hours in counter strike when I started really aim training, and throughout all that time my aim developed a little bit, enough to hit gold pretty easily and start my journey from there. But since I started putting time into voltaic my aim has gotten so much better. With that said, your question is a bit flawed. Aim training will almost always develop your aim way faster than just playing the game, but it won’t give you game sense and game specific knowledge. You’ll just be better at moving your mouse.
2: it would depend on a few factors. First being how new you are you aiming with a mouse. If you’re fairly seasoned and can’t hit iron, there’s probably some sort of problem. It could be with how you use your mouse, how you grip it, if you grip it too tight, if you’re solely relying on your wrist, or it could even be an issue with your setup. Do you have enough room to aim, are your skates super worn down, do you have mouse acceleration turned off? If you’re newer to using a mouse, just give it time.
3: you can just change your sensitivity and see what feels best and what scores higher consistently, there’s no magic answer. It’s just trial and error. And don’t feel like you’re locked to an exact sensitivity between all games. Different games play better with different sensitivities. For example, in cs2 I play at 64cm/360, sometimes higher depending on how I’m feeling and aiming that day, and in the finals, cod, ow2, and whatnot, my sensitivity is between 45-56cm/360. I’m on the lower end of the sensitivity spectrum, a lot of people play a bit higher than I do. Your sens is 26.64cm/360 which is on the high end, though it’s not insanely high. But it is more difficult to be accurate and smooth at higher sensitivities. I’d recommend trying playing around 35-45cm/360 and get used to it, see if you like it more and perform better, but you could train and get pretty good at your current sens.