A bit unfair comparison IMHO.

While Rand may indeed have become an evil tyrant, there is much to excuse it for. I mean the poor guy was insane due to Taint,LTT,horrible stress and probably TP too. Not to mention his semi-rape by Alanna, horrific torture by the AS and the bizarro!bond to Moridin. And lets not forget being in constant pain from the wound given by Ishamael. Or the fact that the Shadar Logoth wound is apparently attempting to reach into his mind and make him paranoid and crazy the way the dagger did to Mat(BS said this I believe).

He can be somewhat forgiven under those grounds. I suspect most people in his place would also have lost it and gone equally crazy. Infact probably sooner than he did.

Tuon has no such excuses. She is stable and sane. She does not have the entire pattern on her shoulders, nor is the pattern forcing her to this way and that since she is not a ta'veren. And while she is a ruler, unlike Rand she was taught and prepared for that role from early childhood.

There is no comparison.