Realistically speaking Animosity shouldn't be in the game at all. It's one of those vestigial "fluff" rule leftovers from earlier Editions. While other armies had similarly ridiculous and detrimental rules streamlined or weeded out (like for example High Elves' Intrigue at Court or the highly restrictive Undead special rules), Animosity inexplicably still remains to this day as the only rule that makes your army worse. This is even more surprising as 8th Edition went to great lengths to make the game more playable. I daresay you could go ahead and simply remove Animosity and O&G still wouldn't be game-breakingly powerful. Furthermore, in my opinion a race being born and bred for war should be reflected in said army being better than others, not worse.