You need to conduct the same test in SP and see how it turns out. MP have issues, but that might be related to the systems in the F-18, and the nature of MP(pings, etc.), rather than the 120. AFAIK there is only one version of each missile that is used across all ED product A/C. 3rd party A/C is a different story.
I do however agree with you that it is very difficult to score a hit with the 120 in MP, driving the Hornet.