A lot of issues here. . .
One, money is always an issue. If you look across the board, you have guys buying new motors all the time, new matched 2400 packs or 3000 packes at the highest numbers every 6 months or less, shoot, just look at all the graphite out there. All to gain a little advantage and lose a little weight. If you have the money, you'll spend it. It's one reason that I have been racint Pro10 around here. . .much less that I need to spend. (not saying that you CAN'T spend as much on Pro10, just that I don't feel that I NEED to.)
Two, just as the 1/12th guys (and oval) know, you can make a motor run as long as you want with the proper gearing and brushes. It may mean a sacrifice in lap times and top speed, but it CAN be done.
Three, I haven't ever seen 1700's run for 5 minutes with any kind of competitiveness. Maybe for the first 2 minutes, but as high as we gear stock, they just don't have the capacity to go that long. Here at SoCal, I don't think that anyone running in the A or B main runs anything but 24's or 3000's except in practice. We've done comparisons between them, straight up, and without fail they just kick anything less.
Four, 19 turn - why is a 19 turn motor going to last longer than a 27 turn motor? They pull more power than a 27 turn, etc.
But, my two cents -
The average battery (2400, 3000) can make 5 minutes with time to spare, so let Rookie and Intermediate run that. It would take more thought and preparation to make 6 minutes competitively so let Sportsman (privateer) and Expert (sponsored) run 6 minutes.
As long as money can purchase cells that give an advantage, motors and lathes that can give an advantage, chargers that can give an advantage and car kits and parts that can give an advantage (given equal skill levels and setups of course. . .) then our sport will, generally, always be about how much spent.
I would LOVE to see a spec class take hold (other than 19 turn, thanx) that would have any kind of a chance to reverse this trend.
Just my two cents.