It is (RER E, Magenta station), but Métro connections are likely more important than a RER one (people who will need to take the RER are likely going to the suburbs and so they will have taken directly a taxi from CDG).
I also agree that Gare de l'est is not the best choice and that they could have rather chosen Haussman-St Lazare, by joining the RER E tracks near Gare du Nord and Est. This would have involved limited underground constructions and will have make the line arriving in a much more attractive and interesting location for business pax and tourists. But to be fair, whatever the terminal station is, you will always have people happy and other unhappy