.50's are the opposite of worthless. Back in Korea the .50's could pump out 900-ish rounds a min. Each round had a muzzle velocity of over 2800 feet per second. Each round weighed 619 grains and impacted with over 10,000lbs of energy. The Browning M2 also shoots pretty dead on for a machine gun out to 1500yds, That's twice as far as you'd ever engage an air target.
Now multiply all of that times six.
There's a reason why the US standardized it's armament to using the .50 during WWII. Against heavily armored ground targets it wasn't a great weapon, but against anything in the air it was a rip saw, thousands of pounds of bullets hitting a target so hard that in the words of one Jug pilot engaging a Bf-109 "it moved the enemy fighter visible sidways". Jets, by the nature of their fuel and power plant, are even more susceptible to incoming fire. To say that the .50 is worthless is such a closed minded, uneducated statement. One to one vs a cannon like a 20mm or 30mm sure, a single round doesn't do the damage, but you never have equal fire lol, you have 10 rds per gun times 6 guns all focused on one little area since the guns have a set convergence for each cannon round.....
I think if nothing else you could look at the kill ratio during Korea too. We wrecked their crap lol, I wanna say a 10 to 1 ratio (fuzzy memory).....most of the kills are owned by Sabres, and of course these were equipped with 6 x M2 .50 cal. Were there other factors contributing? Yep, hydraulically boosted controls and better visibility on the Sabre sure were clear advantages over the MiG-15, but once in a position to engage you had your .50's :-)