Lets look at different combats at a more RL historical standpoint.
Altmer VS Bretons: The wars against the Native Americans are a good example of what might happen. The Breton would invade Summerset Isle and decimate the Altmer with their magic resistance and the Altmer's magic weakness. Against other mages, Altmer would lose any battle. Basically, the Bosmer have better weapons, better defenses, and would easily dominate the Summerset Isles.
You're missing an important fact though, Altmer outlive Bretons, they still have arguably the most powerful mages
in lore due to their long lifespans allowing them considerably more studying time. In Morrowind/ Oblivion 1vs1, yeah, I'd give it to the Breton no contest, but large scale war from a lore standpoint is different and their weaknesses/ resists are subject to change. I'm assuming they'll each have different racials in Skyrim than in previous games.
From the UESP -
The High Elves are among the longest living and most intelligent races of Tamriel. Because of this they often become powerful magic users, having centuries in which to practice their art. Due to their incredibly strong minds, some Altmer are naturally immune to paralysis, both natural and magical.