Originally posted by btnapa User error is out. I have been shooting for too long for user error.
I have been shooting since the late 1960s, but I don't know that I would ever make a claim of inerrancy based on those 45+ years. I don't doubt that you got poor results, but your deep experience was not with your K-3 and you did not attempt the same subject with the superior Canon system that you no longer shoot with. I have several friends who shoot Canon semi-professionally and none brag about the AF system. What I generally hear is cursing. For birds in flight when shooting Canon, the general appraisal is that the lack of accuracy is balanced by the fast frame rate. Spray and pray and blame the gear at end of day.
In regards to your wedding...Were you shooting your FA Limiteds wide open? Are you aware that NO PDAF system on the market has focus sensitivity greater than f/2.8? Were you shooting AF-C? Shoot AF at wider than f/2.8, even using the center column of sensors and your keeper rate will fall. Shoot AF at wider than f/2.8 using other than the center column of sensors and you keeper rate will fall significantly. Shoot AF-C in dim light and you are asking for failure. The K-3 has exceptional capabilities in this area, but the system will be slow to acquire focus and AF-C is contraindicated. Even Nikon has trouble with this use case. A pro would have tested the room prior to the ceremony and bumped the ISO high enough to allow a narrower aperture. Lecture over. Sorry you missed your shots. It is a disappointment when that happens and it happens even to experienced photographers.
As for the slowness of the SDM motors in some Pentax lenses, I would refer you to the reviews on this site regarding focus speed. The SDM lenses are very quiet, but notoriously slow. I wish it were not so and am embarrassed for Pentax that they still don't have a speedy in-camera AF drive system.
Steve