There's more to it than just 'he's mean to Ty'. I wasn't going to weigh in since Grizz knows my issues with Roswell and it doesn't involve how he treats Tyson. I remember you saying you only started reading relatively recently but the Roswell being disliked issue isn't a recent development and Grizz has rewriten him ALOT really.
In the beginning Roswell would out right insult dave and treat him like a useless child infront of everyone. Then there was all the inconsistencies with things he says and how he would act and Grizz had trouble making him flow propperly which made Roswell come off as malicious and manipulative. Such as how everyone calls out Dave inviting Tyson without asking as a dick move. But then Roswell keeps quite about how he feels about it for about 12 days then when he tells Dave his secret he then uses it as amunition against Dave as if it was never brought up. Considering that Dave is reeling from just being told Roswells secret and is already overwhelmed he then decided to bring up any baggage and issues he has against Dave at the same time. It looks incredibly calculated and manipulative.
Grizz has been working on Roswell's issues over time and so Roswell has changed alot over time. However password is rather an 'old' project now most people who read,watch and fund it have been here a while and so they was exposed to 'asshole Roswell'.
Roswell has changed but first impressions matter. While he's not the same its hard to not think of him as he was then when you read him now. Compared to every other character who has been consistent from the start, Roswells initial iteration has damaged his fanbase as a character. So people just developed more feelings for the other characters, but if Roswell was as he is now back at the start he wouldn't be nearly as disliked.