I think its more for disease.
We just brought home an almost 2 year old collie and we have a 3 year old collie. They got along just fine the first week. In the second week, they had 2 fights, and I mean show your teeth , growling fights. Trying to determine dominance I guess, 2 intact females. Haven't had a run-in since. They're best buddies now.
I'm just saying an initial meeting at the pound may not be a good indication. That is not "your" dogs home. Once you would bring the pound or rescue dog home into "your" dogs territory it might be a different story.
We brought our now 3 year old collie home when my other 2 were 11 and 13. The 13 yo loved the new pup the 11 yo wasn't happy with her. But they adapted, most dogs will. They may never be friends, but they'll tolerate each other.