I only watched the first few seasons of IASIP, but I don’t remember them being sympathetic characters at all. The whole concept, and what made it funny, I thought, is that they really are all terrible people who just drag each other down.
It would be disturbing to find out people sympathize with the IASIP characters.
Yeah, the conceit of Seinfeld was that the characters were crappy, but you liked them because they were funny. But they didn't actually lean into that as hard as, say, the finale would suggest. All of the characters have something sympathetic that you can like about them, even if you can buy the thesis that they are unsympathetic broadly.
The genius of IASIP is to just lean all the way into this trope. The characters are never sympathetic and never redeem themselves. It's almost an experiment in whether you can make people feel sympathetic toward awful (but entertaining) characters just through long familiarity with them. (Yes.)