You can debate the science all day but the bottom line is what the top athletes actually do. Almost all top endurance athletes, regardless of sport, have trained, and train today, with relatively high mileage/yardage programs. Sure, maybe some programs emphasize quality over quantity but they're still doing a lot. To take but one example, in the '08 Oly each day in addition to his roughly 22 prelim, semi, and final swims, Phelps swam several warm-up and cool-down swims each day totaling 7500-8000 m per day. He could consider this a "light workload" b/c he was used to going around 16,000-18,000 m/day during heavy training, plus dry-land and weight training. The greatest swimmer to date certainly was not just skating by on just "low volume, high quality" workouts.
To go back the OP's question, I don't think there is any such thing as junk miles or yards. Every single 100 you swim makes you a better swimmer, every single mile you run or bike makes you a better runner or cyclist. Sure, swimming, biking, and running big volume wears you out but it makes you much stronger. You train hard and long for months, then taper, then BOOM, you're going faster. :)
"Anyone can be who they want to be IF they have the HUNGER and the DRIVE."
To go back the OP's question, I don't think there is any such thing as junk miles or yards. Every single 100 you swim makes you a better swimmer, every single mile you run or bike makes you a better runner or cyclist. Sure, swimming, biking, and running big volume wears you out but it makes you much stronger. You train hard and long for months, then taper, then BOOM, you're going faster. :)
"Anyone can be who they want to be IF they have the HUNGER and the DRIVE."