What you experienced on RCI website is correct and I experienced the same thing when I was looking to book my cruise in August 2019. This will be our first RCI cruise and haven't had a lot of experience with their website. I chose the option to pick my room, however there was never an option to choose my room number. I called them personally to book the room instead of using the website to finish my booking.
Being an experienced Carnival cruiser, I knew something wasn't right with the website. I use Carnival's website to find prices and rooms available. Then, I call my Carnival TA to book the room. I truly hope you give cruising another chance either with RCI or another cruise line.