You are no doubt correct, but at the end of the day perhaps in the interest of customer satisfaction, Roku might want to contact PLEX about their app. The reason we purchase Roku's is for specific capabilities. When those capabilities fail, customers look around at the competition. I have 2 other brand products, similar to your product, without this Plex issue.
In fact, the current Plex app on Roku now doesn't support the Plex server version I have on my brand new NAS, and there's no way to update it on the NAS until Plex provides a new update. But, if I use your competitor devices, I have full Plex capability. That's not good for Roku, regardless of who is to blame.