That would indeed be fair. On the other hand, I couldn’t repair the clutch on a car on my own whereas taking a bike apart and putting it back together can be done in my living room if need be.

On DIY: absolutely on anything not safety related. I‘d never touch the brakes. Changing oil is perfectly doable for a reasonably skilled diy person. If you like that kind of thing and have the access to the necessary infrastructure (especially for oil disposal), go for it.

But I like to take the car to a mechanic for another reason: in Germany you’re required to get regular technical inspections (TÜV), if the mechanic does it chances are better that it goes through without problems.