IMO it's very do-able. We did one day, both parks this past August on a very busy day, with really high heat (they were having their crazy heat wave). Now we did stay one night on site so we could get early entry into Studios to ride Crush's right away (since it has slow lines and no Fast Pass), but you might be able to manage it with single rider line (still a sizable wait)
But we were able to get through the following:
Studios:
Crush's
Ratatouille
Rock n Roller Coaster
Tower of Terror (x2, we hopped back to studios later in the day for a second ride)
DLP:
Indiana Jones Coaster
Pirates
Small World
Big Thunder Mountain (Fast Pass #1)
Hyperspace Mountain (Fast Pass #2)
Star Tours x2 (once with FastPass #3, Once Without)
We also toured through areas that had no wait times like Alice's Labyrinth and the Nautilus Ship
We were a family of 4 with 2 boys who like the more thrilling rides, so we didn't do any "princess stuff" and skipped the more "younger kids" rides, but we felt we got to do everything we wanted (minus Phantom Manor as it was closed).
And this was all by 5:30 pm. With the extreme heat going on, we were exhausted by this time and decided we had enough. France normally isn't crazy hot in the summer, so if you're planning on doing rope drop to close, IMO both parks are very do-able in one day if you're efficient and don't need to see/do absolutely everything.