Personal experience only... I'm righty. Bowl on 5 man team, on higher friction surfaces with a medium volume easy house shot. I average around 215. My league has maybe 10 lefties out of 90 bowlers. That's about 1.1 per pair on average. On weeks when I am travelling for work, the league allows me to prebowl, usually on Sunday mornings. I call ahead to notify and they put down a fresh shot for me. When I bowl alone on a fresh pair (granted this is on 18 games), I'm averaging 233. Why? Well, over the course of 3 games when I bowl by myself, I generally have to move 2 to 3 boards left over 3 games. I'm not changing angles, not changing breakpoint...if I miss the pocket, I just threw an awful shot. That's the truth. If spare shooting was a little better I'd average 250+.
On a regular league night with 9 righties on the pair, I generally adjust 3/2 between frames 1 and 4, another 3/2 through game 1. In game 2 when transition really hits, I generally jump another board left every other frame through the end of the game. Usually, I have changed angles.so much that either I need to be very accurate with shots OR, it's 10 pin, 2-8-10, or 4 pin. Ball change and who knows what happens. By game 3, I'm usually 15 to 20 boards left, playing a completely different part of the lane, fighting over reaction. The lone lefty is still playing up 10, wiping oil rings off his ball each frame.
There is a clear advantage, just from the traffic point of view. Also, related to traffic is lane surface. Pristine lane surface gives better, more consistent reaction.
Argue what you like... Don't know how to play the lanes, whatever. When you can stand in the same spot and throw in the same zone, over the course of the night, you are at a clear advantage.
My dream is to one night show up and find out that there are 9 lefties on my pair 😀.