To the OP. there are a few ways to take it.
My pantheon takes Gruumsh as the ultimate traditionalist. He set the laws for the orcs at the beginning of time. You don't use a weapon or armor you didn't make by your own hand. Only weaklings and women use magic, true orcs are strong. Stuff like that.
He has ended up diposed by his Wife, because of the many things, including the war with the dwarves. The Orcs outnumbered the dwarves hundreds of times over, they were stronger, and they were just as tactically saavy thanks to Ilneval.
The dwarves had steel. And healing magic. Luthic begged Gruumsh to bend his rules, to allow her priestesses to heal her dying children so they could win the war. He refused.
Then the goblins swarmed from the West, and the orcs were nearly wiped out. Desperate and driven by fury and grief, Luthic finally betrayed Gruumsh and sealed him away, taking his throne.
I've also seen an idea from Ludicsavant over on GiTP to make Gruumsh the god of equality and the sky, he rages because not all people are yet equal, and wages wars against what he sees as injustice. He is the god of the sky because the sky stretches over all. It is a really interesting concept to see the full pantheon he's laid out.
I think the real problem is that settings like FR and Greyhawk just have too many deities. Especially racial deities.
Unpopular Opinion:
Either have only racial deities or none at all.
Racial deities in D&D just serve to reflect their relationships on mortal beings and subvert their free will. That's the point of this thread.
Evil Gruumsh before just serves as a vehicle for orcs to hate elves and dwarves and rope humans and halflings in the mix as allies. It'san excuse to copy LOTR's racial diplomacy over without the story and premise.
That's why I like
@Kurotowa's Punk Rock Gruumsh. Now his destruction and fury is more sensible and his relationship with the civilized gods makes sense. You can understand wh Gruumsh hates some of them and can make sense of nonorcs following him.
Your unpopular opinion is my bread and butter. I've become convinced that the "greater gods" Like Pelor, Bane, Waukeen, ect ect ect. are really just the
human gods. Because no setting actually has a living, existing "god of humans" (I get why)
But, when you have:
The God of War (take your pick)
The Elven God of War (Vandria Gilmadrith)
The Dwarven God of War (Clangeddin Silverbeard)
The Halfling God of War (Avoreen)
The Gnome God of War (Gaerdal Ironhand)
The Orc God of War (Ilneval)
Suddenly, it makes a whole lot of sense exactly where human deities have to fall.
I dont get peoples fascination with making gods Neutral all of a sudden.
You simply interpret the will and scriptures of your God differently. You use those scriptures to justify all sorts of horrific crimes (pogroms, holy war, execution of apostates and infidels, torture of the unclean etc etc).
For me personally, it is a matter of making sense of the world.
Let us take Nerull. No one sane worships Nerull. They can't. His entire point is that he desires to kill everything. All people, all life, everything. No one sane could say "Hey, death of everthing in the universe? That is my jam"
Meanwhile, you have Pelor. The God of Healing and Agriculture. Hey, are you sick and need healing? Pray to Pelor. Planting a crop? Pray to Pelor. Hey, like the sun? Pray to Pelor.
Everyone would worship him.
But, these two entities are supposed to be equal. One with their occasional cult of madmen, and the other with continent wide constant worship.
So, instead of just tossing Nerull out, we look into remaking him. How can we take this dieity and turn it into something a sane person would believe in and follow? That tends to mean taking evil deities (most of whom have the subtlety of a saturday morning villian) and making them more neutral and nuanced,
I've got a similar reaction to the notion of racial or cultural pantheons. Domain overlap in real-world pantheons occurs because different groups of people told different myths to explain the same natural phenomena. The Greeks came up with Apollo, the Egyptians came up with Ra. If I see the same pattern in a fantasy setting, my first instinct is that the same thing is happening. I feel like if there was a real sun god who was active in the world the way fantasy gods are supposed to be, he'd sort out the truth of the matter pretty quickly.
And if there really are multiple sun gods -- how? And why? That seems seriously to dilute the magnificence of the title. If you piss off Apollo in Greek myth, you are basically screwed: there's nowhere to hide from the freakin' Sun. But if you piss off Fantasy-Apollo in Fantasy-Greece, can you just go to Fantasy-Egypt and hang out under Fantasy-Ra instead? Are there different suns?
You could do some postmodern "all myths are true, belief makes it real" thing where the different realities sort of overlap, and if you can execute that well (see the works of Neil Gaiman) the result can be powerful. But it can also very easily result in a cosmos where nothing matters because it's all just, like, your opinion, man.
One thing I tend to do with this is to avoid making any nature deities. Magic as well. No god or goddess has control of magic. No dieity is the god of the sun or the moon or the sea or storms. That is the realm of nature spirits and the Druids.
So, I don't know who The Sun is, but getting their attention at all is probably a terrible idea, let alone pissing them off.
Instead, I focus on things of society and culture. War, Art, Beauty, Trade, Law, Dreams, Knowledge.