This is a lot of words to say "I don't believe him". None of us really knows, and it's not worth speculating about, because the case is about something much bigger now. It's about the limits of executive authority, separation of powers, and rule of law.
> he did this by almost certainly committing perjury by claiming there were criminal gangs who would kill him if he returned to El Salvador
What evidence is there for this "near certainty"? Your argument here should be with asylum laws, not this individual.
For what it's worth, the situation in El Salvador at the time he left (when he was a minor) does make the claim somewhat credible. There's plenty of evidence that the choice for male youths at that time was leave or join whichever gang controlled your area. The idea that everyone is an "economic migrant" ignores the reality of the situation, which is far more complex.
I don't know in his personal case if he is lying. However, you can get to what the probability of a random applicant for an asylum being truthful very easily. You just need a good estimate of the % of migrants that had to flee gangs or other risk of death (gangs that are still in control of their communities), then compare that to the % that claim they had to flee for those reasons, then subtract.
I don't know what that % is, but we have courts that are deciding these cases every day. The actual court cases are more complex to analyze because lack of adequate council or other factors might influence outcomes. However, of people who attend their interview, about 44% are determined to not have a credible fear.