Of course Eric is a major asshole, nobody doubts that.
But I don't know if you can call it prostitution what he does with Alice, or forced sex-ed with Lisa. They're both doing it of their own free will. Alice wants to be a sugarbaby, and Lisa is curious about sex.
I still think Max is the bigger creep. He installed cameras in all girls rooms without their knowledge and initiates sexual encounters to drive up the viewer count. It would be different if he told his family about it, but he does not.
As you said Eric is a better at manipulating and corrupting the girls, and he has a better aesthetic. It simply makes him more interesting for me to put into situations. Max doesn't work as a good catalyst for corrupting the woman and he never wanted to share, that makes him a bit more boring.
Both men have their pros and cons. As I said, I'll take stories about either one. None of my comments have been about which of them make a better protagonist.
And I'll reiterate a point, we see what Max does 24/7 in the game. We only catch the tiniest glimpses from time to time of Eric's day. And nearly every moment we see him he is doing something rather questionable at best. It's very hard to believe we are catching him at his worst and seeing every single thing he's doing that is creepy.
Also, youth is generally given more leeway to make mistakes and do things they shouldn't. I'm not claiming Max is some 5-year-old with his hand in the cookie jar, but a young person who is curious and peeps is not nearly as creepy as a full grown man who does the identical thing (agreed that peeping isn't the creepiest thing Max has done). Maturity is supposed to come with better judgement and is viewed more harshly when it fails.
But without knowing what Eric is doing at all the times we don't see him, it's really impossible to name which of the two take the creepiness trophy. From an adult story viewpoint they both bring an active sexual context into every venue, which is really the point behind them both.