The Forsaken are confident of their ability to beat one another because they understand this concept. They are reluctant to face each other directly, because they understand this concept! Any fight between any of the Forsaken, and any one of the battles with Rand COULD have gone either way. Rand is largely ignorant of the One Power, even as late as tFoH or aCoS, yet two of the more accomplished Forsaken flee at his approach. Acknowledgement of his greater skill or power? Not in the least, or at least not anymore than taking cover when someone starts firing a gun is a tacit acknowledgement of their superior might - in each case, it is no more than simple prudence. The Forsaken avoid fights for the same reason you would duck and cover if explosions started going off, or a gun was discharged in your vicinity: neither of you cares about the story as a whole, but rather only care that YOUR part in it goes on a bit longer.

A competant channeler's ability is something like a gun. There is a wide range of capabilities, and the skill of individuals in weilding it varies greatly, but in any case, it is ALL sufficient to kill a person. Anyone from Daigian up through Rand has enough strength to kill each other. The issue for each possible permutation of a channeler battle depends on how or whether he or she can bring that power to bear. The problem in the books is that the first real channeler battle anyone noticed was Moghedian letting her bully's ego draw her into an unrealistic and aberrant arm-wrestling match with Nynaeve. What they overlooked was the more accurrately illustrative channeler battle in the previous book - Moiraine vs. Bel'al. What did that fight tell you about their respective strengths?

That's why it's all a crock.