I've seen in other leaderboards, they have sub-categories for campaign difficulties, and I was wondering if this game could have a sub-option for harder difficulty speedruns. Thought it would be fun to do a harder difficulty outside of the easy mode

You can run the game in any difficulty you want, there is a difficulty choice you can select when submitting runs. I'm not sure how much of a difference this makes on the route (as I don't believe anyone has looked into it/ documented differences) but I personally see no reason to add a sub-category unless there is a lot of interest in the category.

I think the enemies have stronger everything(mostly offense and defense) I would need to play it for a bit to see if the AI is more accurate

If you're looking for proof of interest in sub-categories for different difficulties, I would be interested in seeing those sub-categories. I know that one person's interest probably isn't enough to add them, and that's fine, but I figure you'll never know whether there is interest if no one says anything. Cheers,