Thanks for your question. I'm not sure a significant disadvantage is the phrasing I would use. ED gives an applicant an pretty advantage for admissions because you are telling the school you WILL attend which is great for overall yield and is as strong a sign of interest in the program as you can show. However, most applicants will apply RD so it can't be that big of a disadvantage.

Now on the RD timing side even if you submit early your application most likely will not be read until after ED since the AdComm will most likely be still reading ED applications. It is of course still better to get your RD application as early as it is ready given the rolling nature of the CBS application process. But ED is early decision for a reason so those apps are reviewed first.

Hope this helps!