Besides having near identical performance in other categories, the P-38L has a better ordinance package, and that's not debatable.
What's more, at 400mph ias, the 38L is tied for #1 with the 47N for best roll rate in the game, whereas the 38J's roll rate at the same speed is nearly 3x slower. That's also not debatable.
I use the term "clearly" because the pertinent categories are not debatable, and I use "superior" because the 5" rockets are better than the 3.5" rockets, and a faster roll rate is better than a slower roll rate. Hence, the 38L is clearly superior to the 38J.