Seen this thread before, many times....too many to count. Some time ago there was a similar thread in which Norm wrote an excellent reply that encompassed all the things related to superb AF. It was very interesting and most enlightening...wish I could find it and post it here. The bottom line of it was that you can get it....for a price. You can't get a Lexus for the price of a Kia, it is simple enough, but somehow many don't want to recognize the facts of economy that relate to higher prices for more performance.
That said. I'll give you my often posted story. It is 100% true and not meant to be "Fanboy" fabulous, just the facts as I have encountered.
About a year ago my K5IIs was badly damaged in a freak accident. I loved it, best Pentax I had ever owned from the DS forward. Mrs Rupert, seeing I was brokenhearted offered to buy me a K1. Not being a total idiot, I quickly accepted her offer!
Now I have been Bigma 50-500 shooting for over 10 years...from the DS forward through many Pentax bodies. Every new model has "reported" better and faster AF....in most cases it was an illusion at best. I have spent countless hours while the Bigma hunted like a blind hound and my subject didn't wait for me to get a decent focus as the Bigma tried and failed to find focus in a timely manner.
I learned new curse words, threw things over shots I missed, and lived with the general frustration that I read in your post.
This carried over to my newest Bigma HSM OS model....some improvement over the old model, but still the hunting and failure to lock focus fast and sure...in particular in low light or brushy scenes.
So...the K1 arrived and I had a fresh battery ready. I quickly mounted the Bigma and went to work testing the "greatly improved" AF system. First shots of wildlife brought out some of my well used curse words, but in a different direction!
Damn, son of a "gun", this thing is fast and accurate! It ain't no joke, it is like magic over my previous bodies, No hunting, zero, no waiting as it hunts back and forth......just bang with the focus confirmation and fire away! I still pinch myself to make certain I am not dreaming....here a year later!
In wildlife shooting you have only seconds to get a shot most of the time. Excepting the trained squirrels, animals don't sit an pose until you lock focus and snap, they are "off to the races" in just a few seconds. I keep my K1/Bigma on my desk ready to shoot, adjust settings a few time as day to be close to the available light needed. When a shot appears I need 2-4 seconds to pick it up, turn it on and lock focus. I get more keepers than not, and most I miss have no relation to slow or inaccurate AF......more about speed and light or not allowing SR to function.
You will see the underside of a Spanish dove maybe twice a year...maybe. You need to be fast and you need fast AF or you won't capture the very few seconds he is cooling his body with wings up. Few people ever see their colorful underside...I had only a very few seconds to pick up the camera, turn it on and point to get focus. Focus was instant. I got what I wanted.
Many hundreds more fit this same situation. My AF problems have ended with the K1. Even low light makes K1 shooting easy....
ISO 12800 1/80 handheld (ALL of my shots are handheld)
Now I am not a sports or action shooter, but with a fast top notch lens I think the K1 could and would deliver for me in that area without frustration.
I still have failures and not all shots are usable, but rarely is AF a cause of the failure. That's my story, and I'm sticking to it...and I'm sticking to my K1 when it come to the AF system it is the best Pentax has ever offered...and yes, it does cost more, but not that much...in fact it is a genuine bargain!
Best Regards!
Get a K1 and some soap to wash that Canon talk out of your mouth!