The problem is you are comparing them in unrealistic situations. You can't just simply remove specific abilities and then say it is a straight up comparison. There are too many variables during the game to justify some of these comparisons. I will agree that eternal guard are usually overlooked and they even have some favorable matchups; however you can't just ignore magic, shooting, and every other unit on the table.
I have always thought saurus were pretty good core spearmen and they are the same points as eternal guard. If you run those numbers then the saurus kill 5 eternal guard and the guard will kill 2 saurus in the first round of combat.
Honestly, I really wish eternal guard were much better than they are, but I just don't think they are.