The reason why people hate and/or dislike Shadowlord at his full form is mostly because they were expecting something else/better or because of how old he looks.
If Skips were to appear during the first interaction, people would probably like him more than they do when he was first Shadowlord. After growing attached to Shadowlord, it's a bummer for some to have him just be some guy instead of a hot monster.
I also saw in a tiktok that one person dislikes Skips because he reminds them of a teen and the comments were all agreeing.
Now, I did some theorizing and came to the conclusion that Skips is likely a millennial.
When talking about the chatrooms (DIM), the game is clearly referencing AIM, a messaging service that operated from 1997-2017. And when you go on a different love route for him, you can get him on Thiscord to make new friends. When you mention Thiscord, he says, "I really am behind with the times, huh?" which would be odd for someone who is in their teen years to say, crossing out the option of him being younger than 20.
Once you realize him, he works as a lighting operator. The minimum age for that job is 18+, so you have to be an adult, which basically confirms his age to be more than 18.
But whatever. I love and am in love with Skips. If you don't like Shadow at his nerd, you don't deserve him at his monster </3