Guess I'll be the contrarian for the moment, then post my numbers. I think you have to start with the concepts of golf and golf course. A golf course is not just a plot of land divided into holes that are defined by tee boxes and greens with holes into which flags can be placed when unplugged. One could hit golf balls with clubs on such terrain, but that doesn't make what one is doing playing golf. Golf courses are designed around an architect's goals and intentions, presumably driven by some conception of the distinctive character of what it is to play golf, why it is interesting to people to play it, what is exciting, mentally as well as physically demanding of it, and much more. I have played lots of courses, but regret to say that too few are designed by architects who understand golf, or rather, are the joint efforts of architects and others (housing developers, resort owners, business persons, etc.) with complex and not always fully compatible goals. If you take a well conceived golf course of any sort, and then just mark off distances back from the green to a place that represents a 'doable' ratio for this or that golfer, you may be hitting balls on a golf course, but you are not playing that golf course. You are engaged in some other activity. I am not denigrating that activity.
On the other hand, hacking one's way around a well designed golf course from the existing set of tees is a nightmare for many of those who play those courses; and it is fair to say they are doing something on the golf course that involves swinging clubs and sometimes hitting balls, but rarely constituting playing golf.
There has to be a better meshing of the two concepts -- playing golf and doing so on a golf course. there are several possible solutions, none of them fully satisfactory or likely to work financially or otherwise. Architects can build courses that are much shorter (given the aging golf population) that are loaded with character and test the relevant skills, etc. This can surely be done as some of the best courses I have played have been 9 hole par three courses. There is a particularly good one in Scottsdale, AZ. These can be expanded in design to include one or two par 4s and even a shortish par five. Problem is golf courses are expensive to build and one has to sell the golfing public on the desirability of playing those courses rather than Shinecock Hills and Oakmont. I have been a serious and at one time top flight amateur golfer my entire life, and have played both of those courses twice and they are not enjoyable: period. For anyone. Shinecock is for people who have the mentality of those who work at Goldman Sachs, where the joy is in the battle and everything is war.
There are executive courses everywhere, but the fact is it looks like most players need to play even shorter courses. It would be worth uncovering data on how many executive courses there are, where they are located and their relative success.
The next possibility is to change the golfer's mentality and expectations. Good luck.
Here's a solution I would think worth investigation: recalibrating par to reflect distances that people actually hit balls. The same hole would have different par ratings. Take a 280 yard hole. For those whose driving distances exceed 300, this is a long and probably relatively unenjoyable par 3. For me it would be a very short par 4. For others it would be an average par 4; and for still others a demanding par 4. Take a hole of 425. For a pro it is a shortish par 4 depending on other factors. For me, it would be a very demanding par 4; and for lots of others a par 5. For me once a hole got above 460 it would be a shortish par 5; and so on.
One might object that the handicap system already does precisely this. I disagree. There is all the difference in the world psychologically and emotionally (which I believe will translate into performance) between a handicap which indicates a 'failure to measure up to the standard' and a recalculation of the standard that has as a consequence turning the failure under one description to a success under the other. And given how much more fluent we are at analyzing and collecting data, there is no reason not to experiment with a more fine-grained formulation of 'par' on a given hole.
There is another step to take that has more to do with reducing time of play and increasing enjoyment as such. Every course should adopt a rule that each golfer (who is a member or a regular) must begin playing the course from the shortest existing tee boxes until he or she can break 80 or 85 regularly. At that point only, the person gets to move back to the next set of tees and so on. the process reverses as the player's capacity to break 80/85 decreases.
My approach to playing golf courses has been as follows. I am now 72 yrs old but am quite fit if not quite as strong as I once was (which was never that strong to begin with. In my hey day, I was say I was Mike Reid long :-). I played the championship tees at all courses up to7k yds until I was 60; then moved to the Blues up to 6700 yds (sometimes mixing and matching to make sure I didn't exceed that by occasionally playing a hole from the whites or members tees) then at 70 I started playing by distance overall. I play a variety of tees when necessary to make the course interesting and to keep it within my sweet spot of between 6100-6500. I just don't enjoy playing longer because I am not putting enough of my clubs to use. I know pros are playing for money so they want to hit as many wedges as possible. I'm really good with wedges, but I am not playing for money or a livelihood. I have a similar lack of interest in hitting 3 hybrids or fairway woods into every par 4. So I mix and match and sometimes play holes from tees that make it very hard for me to reach a green in 2 on a par 4, cause it just makes golf more enjoyable that way. But playing a course with a half dozen 420-445 par fours, not so much fun.
I dread the inevitable day when I will feel that way about courses with holes between 380-400 though I know it will come. But for me, I want to play the golf course for as long as i can as the architect imagined it would be with challenges intact and strategies required.
Driver: 215 (on east coast where roll is something that happens on the greens only more often than not)
Length of courses: 6100-6500
Ratio:
I don't think in those terms. I want to play course length where I can aspire with work to keep my handicap in mid single digits.