Well, if it helps that's likely due to Katarina being an absolute pain in the ass about a year or two ago(? Not quite sure on the time frame) and stuff happened and she became a learning tool for new players to learn how to handle assassins similar to Annie and Master Yi. Maybe it was the removal of DFG?
If it helps, I can answer the Katarina thing for ya. The watered down response is "just cc her," the more in-depth response is "Time it right and cc her correctly. Katarina is an excellent learning tool for teamfights: you learn not to waste your cc at the beginning of the teamfight, managing your cooldowns, and using the correct cc on the correct targets at the correct time. For instance, using slows or snares are basically useless on Katarina and will not inhibit most of her kit once she's in range. Use that instead on the tank before they can get in range of your carries and set up a free Katarina ult, instead of stunning the tank like so, so many people do when new to the game. You want to stun Katarina when she's in a bad position (usually during her ult, I guess), or you can get into position to kill her during the duration (usually... when she's not positioned correctly for her team to save her).
Anyway, I think the main reason people don't listen to your Katarina complaints is that, honestly, she's probably the first assassin to give people trouble alongside Master Yi and people eventually learn how to handle her. Fortunately you probably weren't playing in the meta where she was in basically in every game, and thus probably don't have the level of experience some of us do (suffice to say, so many of us were so sick of her shit we practiced and practiced until we could send Katarina mains to the hospital with butthurt). Your complaints are valid, she is quite the annoying champion, but she's probably one of the lower assassins that just requires a bit of experience to learn how to handle. Hence the remarks about your rank (which I am not condoning, mind you!).
Also we're kind of in a somewhat cc heavy and carry meta, which isn't too good for Katarina. Bruisers kind of kick assassin ass.