Rich,
In some respects, I think your question is invalid because of it's wide sweep.
I consider myself to be reasonably proficient with all of my firearms (both handguns and rifles) with the caveat that each is mission specific and should be judged by a yard stick calibrated to the mission each arm is acquired for.
For Bullseye matches (currently called Precision Pistol), my K22, K38, and 1911 deliver 85-90% performance over the 25 yard and 50 yard courses of fire. For PPC, my vintage K38, and my assorted semi-auto pistols are delivering 93+% performance. For the GSSF matches, my chosen Glocks are putting me in the 75 -100 second time zones, depending upon which division I'm shooting. For F class mid-range (600 yards) and long-range (1000 yard) matches, my preferred rifle and cartridge combinations are placing me in the 88-92% average zones, despite my physical challenges.
For bullseye matches, I shoot my revolvers SA. For PPC, I shoot my revolvers DA, but I wouldn't think of using my 3T bullseye K38 for PPC, because of the wide trigger. When I first attempted IHMSA matches about 40 years ago, I shot my N frame SA (I'd love to find a club within 150 miles or so still doing these matches).
The bottom line is that each firearm and each discipline requires a certain degree of practice. Some practice is transferable, some isn't. For me, I find that timed and rapid fire bullseye is providing the most transferable skills for PPC. Bullseye and PPC are providing the best transferable skills for GSSF matches. I am seeing the best transferable skill development for the Adaptive Defensive Shooting Summit events being PPC and GSSF matches (I tend to joke that the ADSS matches are IDPA:GSSF matches: stationary [like GSSF], but fired on an IDPA-style course of fire).
Being disabled, I strive for consistency using a mission appropriate yardstick. My key concerns are trigger control and focusing on the front sight.