That used to be true at one time but that's the beauty of a properly tuned drop a way rest.In my experience,certain vanes definately promote better flight than feathers if you get 100% clearance.Otherwise,I agree with you.
Fletch,think about two things.First,a properly tuned arrow will spin in flight.If the arrow is spinning,how can it make a differance if the blades are aligned with the fletching?Second,how would you align the fletch with a four bladed head?It's an old wives tail.
Use good form,use the right spined arrow,make sure the broadhead is aligned on the shaft so it spins true,make sure you don't have fletch contact and tune the bow so the arrow is leaving the bow strait.If you do that,you'' get excellent arrow flight at any speed.
I replace my strings and cable every spring with a good custom set.I shoot a bunch of shots with it before I set my peep.With todays string materials,it takes way less time to shoot a string in,usually less than 30 shots but I take at least 50 to make sure.the next day,I set my peep,paper tune and then tune my broadheads.Usually within less than a half hour,I'm all set.I keep two BH tipped arrow in my quiver all summer and take a few shots every time I practice.That promotes confidence,which is paramount.Don't wait until the week befor ethe season.