Did they seriously reduce Arthas to 35 anima and have Sylvanas say he'll never be remembered?!

Wrong, if you saw some one you loved or some one who you hurt and you knew they where about to fade from all existence you would say something.

Uther forgave Arthas but it was also Uthers fault that Arthas is fading away for ever.

Jaina Loved Arthas and she also would 100% say something.