personally, i cant live without midranges (rocs in my case, though i have tried almost all mids). for my game, I have developed a strategy where unless i am putting or really close to the basket (<150'), I am always trying to throw with the same form and power. Using this strategy, in order to get my shots to land within a reasonable distance relative to where i want them, I need those mids for when my wizards are too short and my leopards are too long. by developing this game plan i have found that my form developed much faster and my consistency went way up. Now granted, for a 275' shots, i could easily take out my new champ leopard and throw it 70% and watch it fade and skip, or i could take out a beat roc, throw it with the 85-90% power with which i throw all my shots, and watch it do exactly what i wanted with no adjustment. Adjusting to throwing a disc longer or shorter than it is intended created lots of consistency issues for me.
Also, i think one of the very important and very overlooked aspects of the argument FOR midranges is the added stability in the wind. Again, throwing 275', you could throw a gazelle 70% or a roc 90%. In this case, with no wind, they will fly similarly and land pretty close to one another. Add a 15 mph wind, and the midrange will stay MUCH more consistent and predictable than the fairway driver. the slower fairway drivers (leopard, gazelle, cheetah) just cant fight that kind of wind, no matter what the weight or how new they are (i have found this to be the case from my own experience with all 3 listed above). Stable midranges (rocs, wasps, sentinels...especially sentinels) have the wind-fighting ability to stay on line and remain predictable in almost all weather conditions.
Overall, I think it is possible to develop a game revolving around just fairway drivers and putters, but it is my personal opinion that my midrange game is one of the major reasons i have imporved as much as i have over the past year or so (paired with all the help and advice i have received on this board)
i am not, nor have i ever claimed to be, a top pro or an expert in any way on the sport, but i can speak from my own experiences, and thats all i have to offer here
HOLY RUN ON SENTENCE, BATMAN!