Sure, practicing does make you better at something, but perfect? Perfection is a pretty huge thing to try and attain. I played the flute when I was younger, and I practiced a lot. But I don't think I could say I was ever perfect. I did ballet too, and competitive swimming, and despite practicing both until my muscles ached and I was dropping off to sleep over my dinner plate, I don't think I could say I was perfect.
The same thing can apply to writing. That first book I wrote? Honestly? It stinks. It was a practice book. The next one is better. Marginally. The third? Better still. Now I'm getting ready to start my 7th book. Seven? Wow! I've written six whole novels, and at this stage, I'd have to say they were all practice.
But I'm getting better. Not perfect, but improving. The first book I queried (the 3rd I wrote) got no bites, and quite justifiably. It wasn't good enough. The third book I've been querying (book #5) has had a much better response. Whether it's because I've gotten better at writing queries, or if it's because the book is better is moot. Either way, practicing has helped.
So, how many more before I'm perfect? Well, I don't believe in perfect. I just believe in improving.
What about you? Can you see how much your writing is improving with each book you write?