Plenty of people do things wrong, it doesn't matter how long you've been doing them if they are wrong.

Leaving residue of solvents or cleaning gels in your bore can never be a good thing, they can damage your bore. It's a fact that cleaning with a brush doesn't remove all copper (nor do you want it to) and any 5th grade science student knows that if copper is exposed to air it will oxidize (that green stuff),which if allowed to continue will pit your bore.Hence this is where the oil comes in. This prevents rust or other oxidizing processes from damaging your bore. It's never a bad idea even if you think it does nothing it still doesn't hurt and oxidizing or rust of any kind is your enemy. People tend to focus more on the exterior mainly because it gets wet and it's easy to visually see rust beginning. It's not always so apparent in your bore.

Follow what your owners manual says. If it says your gun need periodic maintenance then do it. It's the same as a car. You wouldn't go two years without washing your car. Your gun is a precision instrument that requires periodic maintenance to perform to it's fullest, regardless of whether you think so or not.