I'm just wondering if you have it set to 60 FPS? Some games have their AI tied to your frames, and I've noticed that older games uncapped can sometimes have results as you describe. Halo Reach for example, in the MCC, was almost impossible for me to complete on Legendary due to the space combat in Long Night of Solace, and the enemies aggressiveness being tied to the game running at 60 FPS as I soon found out. Lo and behold, I locked my game to 30 FPS using Nvidia, and I hardly struggled.
Viewing post in No One Lives Forever 1 - Modernizer comments
I did have the game running at 60fps with vsync enabled with both the modernizer, and without.
I don't believe it has something to do with the fps however, simply because without the modernizer it was a lot easier if it had to do with the a.i. difficulty being "tied in" with the fps then without the mod it would have been equally as difficult as with it installed.
It's a good thing to know for Halo though, I've recently been wanting to replay the games on legendary as well, so thanks for the advice.