I know we don't have official numbers from Disney which I why it's hard say anything with extreme confidence.
I just really find it hard to believe that FP would increase efficiency at omnimover type attractions. I truly believe it doesn't. Look at haunted mansion for example. With FP wait times increased. Same with Pirates. Those attractions should be continually loading they should stop the standby line to let FP in then switch back. Newer rides built for FP are different but it is my belief that rides built Pre FP shouldn't have it because they were built with that in mind.
FP has created efficiencies, not necessarily in the manner you're thinking.
In a given summer day, I might spend 10 hours at the parks. 20 years ago, if I wanted to ride three of the most popular attractions, it'd eat 4-5 hours of my time (or 40%-50% of my day). Obviously with FP, that number is much smaller.
It'd be one thing if it caused a spill over onto all other attractions... but it hasn't. That's partially do to Disney adding attractions & entertainment (re: capacity) and increases in technology (FP, real-time waits on the app -- as opposed to numbers that were completely incorrect, etc.) that help us more efficiently plan our day.
AK does have a good amount of entertainment though. You have rides, then you have shows, walk through animal treks, and more. The general guest just wants rides. Theme parks are not just about rides they have a bit of everything. Just because a park doesn't have a lot of rides doesn't mean it has a capacity problem. Rides, shows, restaurants and more all work together for capacity. You are simply just looking at ride capacity.
No, I was referring the AK when it initially opened. There was very little to do and Disney knew that, creating the band-aid that was Camp Mickey Minnie (not that it helped much). In order to prop attendance, WDW gave complimentary AK admission to many of its convention guests (as opposed to the after 4/5PM Epcot & Studios tickets that still cost 2/3 of the admission price).
And I would consider "capacity" to be anything that draws the attention of the guests.