The CT raids weren't always mandatory, but they have been made so now. I quit playing regularly after HW and would only come back for patch content and EPs so I was also in the boat of not having done CT since whenever it was released (2013?) And I wasn't aware that Yoshi had suggested that everyone refresh themselves on that content before going into ShB. As a result I had no idea who the Exarch was on my first time through and even when his face was revealed I was still lost because, yknow, it had been quite a few years for me. I loved ShB but I was bummed at the time that that moment didn't have as much impact as it could have had.

But with that being said, it is now part of the MSQ and is no longer optional content. So that shouldn't be an issue for newer players.