It's not as if the other characters...don't have a personality?
It's Tomoko, anyone who hangs with her is cringe or has some serious problems, one girl is a repressed homophobe that refuses to accept she is a lesbian, another is even more awkward than Tomoko, another is so annoying she is being bullied by every girl other than Tomoko and so forth.
While their flaws aren't always being shown, they do have flaws that cause problems from time to time, and a lot of it is just in the background or only seen by the art rather than being said, even that twintail girl in the anime that sometimes talked to Tomoko:

Ends up being revealed to have been a major loner during middle school who had a high school debut changing her entire personality and look just to have someone liking her, constantly lying to everyone around her and the main reason why she even talked to Tomoko was because she was kinda suprised Tomoko could be so weird and open about how she is really like while she tries to hide everything.
And that is with her secrets being a lot less bad, her main problem is that she is an otaku with a major love for slice of life anime, hence her anime like hair style when compared to everyone else, and being a bit sadistic and scary when actually angry at Tomoko to the point of shutting her up a few times just with her glare:

Though eventually she reveals her true self and loses some friends while making others incredibly mad that she was just pretending all this time, Tomoko even only found she was an otaku by accident.
Seriously, a big part of the reason why the series became popular again is because the new characters do have traits of their own, and are more interesting than the old ones, to a point where even fan service character Yuu stopped appearing, with the only such characters being Yoshida and Asuka, and Yoshida never even does anything with her body while the joke with Asuka is that her acting like a fanservice character from an anime creeps everyone out, even Tomoko.