Back when Misty was in the anime, they focused solely on Ash. So no one got any type of fair treatment up until we got May and Dawn. I feel like Iris fell more into this same pattern, even more so than Misty, because they had very little care to focus on other trainers.
So to answer your question. Yes. She was. But so was Iris. And while Serena didn't have a goal, she did have story.
With Misty, her pokemon had no growth except Togepie which wasn't even a water type and kinda took over her pokemon screen time like you mentioned.. And a smaller note was Politoed. She completely neglects most of her other pokemon. Misty at least did have a few centric episodes later on, but she was still very neglected. Her only big leap in becoming a Water Master was winning the Whirl Cup, returning to the gym and releasing Togepie.
People need to remember that there was never supposed to be any more episode after Johto, but that was retconned when it exploded in popularity. Iris was shafted even more though. She only has three dragon pokemon. One in which most dub watchers won't even know about and didn't show up in Journeys except in like a flashback. She was basically a copy and paste of Misty. Wanted to be a Dragon Master and was afraid of ice pokemon, but in a worse manner.
Pokemon was already popular before Johto, so to me there always was gonna be episodes afterwards.
But anyway, I think they just didn't have a clue on how to focus on Misty and Brock...