I’d agree that they don’t need to develop every one immediately but Perrin more then any one else is quite and slow for a large portion of the early books. In a book I think this works just fine but in a show it’s a lot more awkward.
If the show had like a 15 episode first season and the first 3 or so were all about the two rivers and they made sure to focus on him and how he’s always helping out and being thoughtful if not talkative id say it would be fine but I also think a fantasy show needs faster start to grab none book fans to really get a foot hold.