The writers definitely didn't forget about Eris and her telekinesis. They hoped the audience would, though. And most did forget it.
I'm one of those people who forgot about it. I watched the whole series last year for the first time on Netflix, and somehow I forgot about that ability when they picked up that thread again. It's funny, because I'm watching the series again (this time with my wife), and this time when I saw that energy shoot out of that Vorta's chest, I thought...wow, I guess the writers decided to drop that idea. But then again, my wife is always reminding me how awful my memory is!