That's not true at all, get your fact straight.
20/(16/55) is 68 bullets in average.
Since you want too be accurate and are so fond of "empirical evidences" (can you please list those ?) let's check actual 50 cal ROF.
http://www.stat.coh2.hu/weapon.php?filename=m2hb_50cal_mp
50 cal fires 5.88 bullets per seconds, and if it takes 68 bullets to kill a full health luchs, than it kills a full health luchs in 11.56 seconds.
The 50 cal used with snares is an extremely viable luchs counter.
"...the fact that he would claim that even with the numbers that he cited is...willfully ignorant at best..."
I translated my liutenent builds experience into the discussion, supporting it with proper stats...
And apparently it fires 8-9(?) bullets per burst, with 3 seconds in between bursts at max range. So it takes around 1.5 seconds to fire off a burst, and 3 seconds in between each burst. Since it takes 68 bullets on average (yeah, I calculated that wrong, not sure how, but thank you for correcting me) to destroy a luchs, you're looking at around 8 bursts to destroy a luchs. Thats 7 * (1.5 + 3.0) + 1.5 seconds to destroy a luchs (no cooldown time to fire off the first burst). That 33 seconds to destroy a luchs, not even counting the time it takes for the reload you have to do once you activate ap rounds or the reloads you'll have to do afterwards, or the initial aim time. I don't quite see how you could argue that the .50 counters a luchs when it takes more than 30 seconds on average to destroy one.
For perspective, the M1 AT gun takes about 8 seconds to destroy a luchs, not counting aim time. If the luchs has already taken 100 damage from a snare, it only takes 4 seconds. I could factor in accuracy, but whether or not the shots would actually land is not honestly that relevant overall because players always play around the ~30% chance that all shots land. You counter the luchs with the just the threat that its possible (and honestly pretty likely) to destroy it in 8 seconds.
Tl;dr: The m1 is a counter to the luchs. You can threaten the enemy with the idea that they'll lose their luchs in 8 seconds from 60 range away. The .50 is not a counter because it requires the luchs to sit laughably close to an easily circleable weapon team for over 30 seconds, more than 4 times the time it would need to sit in front of an m1 AT gun.
Side note: another technicality that you can't model with stats is the fact that if you circle a .50 with your luchs, even if he predicts your movement and gets you back in the arc (maybe you got AT naded), youre taking maybe 3-4 bullets before you get back out, which is around 20 damage (once you consider penetration vs armor, of course). When trying to circle an m1 at gun, if you mess up, you take 160 damage. Also, the m1 at gun's crew gets heavy cover, making it much riskier and take much longer to decrew it. Finally, if you decrew the at gun, then he can recrew it and go back to firing it and forcing you to circle it again. If you decrew the .50, i'm *pretty sure* that he has to spend more munitions again AND go through another reload before he can begin damaging your luchs again.