what if I get more productive but level out and lose creative drive?

that is not how it works, unless being more productive inherently makes you lose creative drive for some reason. also being diagnosed doesn't mean you have to "change your brain"

increased productivity allows me to spend way more of my time actually doing the creative stuff than i do with worse productivity

I'd say it depends on how you think it's affecting your life*. Everyone has some symptoms of adhd the difference is the full picture and your ability to control it. Nobody likes boring tasks and everyone has trouble with motivation, at some level it becomes symptomatic of adhd but the way to figure that out is through a doctor and trying different treatments.

*interesting thing about what's classified as a mental illness is that it needs to have a negative effect on your life. There's debate about things like narcissism being an "illness" because often it actually helps the person succeed, and they would never think of themselves as being negatively affected by it. If our society rewards a condition like this, what does that mean for classification of mental illness and how medicine is practiced? Similar questions apply to adhd, I had a job that exploited my adhd very well for a long time and figured if I had it then whatever that's just me. It wasn't until it was a serious issue that I decided I actually need to figure out if I have it and try something.

Getting diagnosed, it might be an eye opening experience. Symptoms and connecting them to your own personal life, like no shit I'm a walking talking barely dysfunctional bag of flesh but this explains why.