My wife and I just returned from Normandy yesterday. We used both Isislines and Ouibus booked through the Ouibus app to get from CDG to Rouen and return to CDG from Rouen. Trains would have been better but when we booked the buses it was to avoid any problem with the strikes and the trains. I don't recommend using the bus, though it is incredibly inexpensive (18 euros for the both of us each way), but imo, it is not user friendly. Once on the bus, everything is fine, A/C is good, and the buses make great time on the peage(toll ways), but the CDG to Rouen trip also stopped in downtown Paris for passengers and the waiting time was equal to the travel time of about 1 ½ hours. And, there is virtually no information at the stations as to where the buses leave from. And, the stop in Rouen is on the street, the so called Gare Routiere, 33 Avenue Champlain. The very low price doesn't make up for the other inconveniences.
For what it's worth, I am guessing the long travel time from CDG to Carn/Bayeux is likely due to using the TGV which goes from CDG to Amiens and then connects to Normandy destinations. I think this because earlier I also tried to book a TGV from CDG to Rouen and culd see on the SNCF map that it went to Amiens first.
My daughter and her family were with us and had to leave our Gite a day earlier than we did for a Eurostar to London. They attempted to leave their car at Rouen, for a train trip to Gare St. Lazare and subsequent transfers to Gare du Nord, but there was a protest (manifestation) that day and the streets in Rouen were so blocked that they ended up driving to Paris and dropping their rental and then using the Metro to get to Gare du Nord, it worked but they were worried about making the connection.