Most overused word in online debate history. Watch a real debate and debaters are very careful to use the term, because usually it amounts to a non-argument. That aside...
I am not assuming a anthrocentric view of the universe. I am saying that the being must love everything of a category equally to be considered omnibenevolent.
I actually think this is a good argument. To be omni-benevolent, it would seem, the being would have to be loving to every single things.
However, if we have an universe with meat eaters and herbivores, it seems to me to defy the laws of non-contradiction that an omni-benevolent being would deprive one animal so it would starve, but protect the other animal so it is not eaten. You might argue, well, get rid of eating meat. Well, have you every eaten meat? It tastes great.
So, now we get into obvious subjective stuff. Is it better that I can enjoy meat but animals suffer, or vice versa?
This is when our inability to actually know what is best prevents us from asserting that we could actually do better if we were all powerful. AN omnsicent being's omnibenevolence cannot look like how we think it would look. That would stand to reason.
So, though you say you are not, you obviously are approaching the problem with man as the center (i.e. perhaps it would be better if God never made carnivores than we can enjoy the taste of meat, this seems to me a human-ethical viewpoint). So, unless you presume humanity and human ethics as moral standards, and then judge a higher being to them, I don't see how you come to your definition of omnibenevolence.
Now my final paragraph here might indeed be a strawman, simply because I am presuming your position. However, let's be honest, what can we objectively say would be better if it didn't exist at all for all of history? Omnibenevolence cannot possibly mean every single thing is good if it in the process negates good things (mercy, meat eating, the movie Twister, etc.) THese things cannot exist apart from the existence of evil.
If it only loved some it would not be omnibenevolent; if it loved no conscious beings, it wouldn't even love itself, much less us and still not be omnibenevolent.
I disagree with the premise, because we already know of acts of love that result from the existence of evil (i.e. forgiveness), so how could a being be omnibenevolent if there are acts of benevolence it will never act upon?
So, I can't tell you this necessitates evil, but I can confidently tell you that we cannot determine that it definitely necessitates the lack of evil either.