Real question is not about ugliness:
"Why can’t we depict an ET more beautiful/handsome than humans?
With our infinite potential for imagination, we are still UNABLE even to depict something better than humans just in physical appearance!?
I still say, who's to say that what has been depicted isn't better?
The point is, how do you know that these depictions aren't better or more beautiful/handsome than humans?
Beauty and handsomeness are subjective. For instance: I love the desert and find it beautiful. I love the cactus, heat, thorns, rock formations, everything about the desert. However, there is likely a large portion of the population that would look at what I call beautiful and say it's horrible, desolate and ugly.
The point is that your initial premise requires bias to be true.
From an unbiased point of view, nothing is beautiful and nothing is ugly. Everything is what it is and nothing more. Beauty and ugliness are just personal tastes.
To say that human depictions of alien races are somehow less beautiful or inferior to humans is a fallacy.
Your biggest problem, abiather, is not looking at things from a rational, objective point of view. Confirmation Bias is written all over your arguments.