I've played a huge lot of HM&M 3, with all its expansions : I then tend to agree with you .. but I played too much of it. I'm burned out in what concerns H3.
HM&M 5 is supposed to be inspired by H3. It is so gorgeous, if your have the videocard & the monitor to display it in its beautiful glory, that I'll play Tribes of the East again, anytime ... but I can't go back to H3.
I agree with you, but I'm finished with that game : H5 spoiled me forever with its gorgeous graphics.
Concerning your Human vs Comp duel issue, I'm surprised : I did play duels against the A.I. two years ago, with the original H5. I'm not interested in duels, so I haven't checked recently. I don't see why you couldn't play a duel against the A.I. Select the proper option from the main menu.