That's NOT what its all about. It's primarily an executive function disorder. Every aspect of day to day life, including the "pleasurable" aspects are affected. ADHD-H the hyperactivity is to increase blood flow to the brain to allow the communication to occur between the problem solving centres of the brain and the executive function. The attention and emotion centres border the executive area and so, depending on the person, they'll end up distracted or they'll become emotional/stressed.
If what you said was even remotely true then that wouldn't explain ADHD-C/ADHD-I (about 30% of diagnoses) ADHD-I can cause you to focus so intently on what you're doing and be unable to switch (be cause the executive function is screwed up) so you'll sit there doing the same thing and plow through. Doesn't matter how boring or how intensely rewarding it is. I'm just coming down off a 37 hour episode of the most mind numbingly inane research that got me zero reward and set me back. I'll take me 48 hours to recover minimum before I can get back to being productive (hopefully). It's great when I spend that time doing something productive like coding but can ruin a week.
Worst part is, I can't control when it happens or what triggers it because things like self discipline and control are regulated by the executive function centre.