I remember the agonies you went through, Ferry, and was truly shocked at the time. I’m sorry you still have ongoing problems. 
I think when making complaints, your starting point has to be pretty much as you say, asking What is my aim here? It could be a variety of reasons such as letting off steam, financial recompense, wishing to see someone brought to book, a desire to stop this ever happening again or simply an apology. I’m sure there are others. Also consider how you would feel in the future if you don’t make a complaint.
My son works in patient safety and complaints are in fact an important aspect of ensuring our services are as safe as possible. There’s a lot of science behind it, in which the patient’s experience is very important.
Only you know your GP practice, though, and what their reaction might be, even though afaik, they’re not allowed to take punitive action against you.