I am new to this forum. I am an avid Judo practitioner (blue belt) and a am very interested in martial arts.
I would have to say that in terms of groundwork, both Judo and BJJ are equivalent. Notwithstanding the fact that BJJ is a derivative of Judo, the two arts differ in their methodology and approach.
Judo has indeed emphasized its sport aspect and as a result, there is little stress on leg and wrist locks, which are prominent in BJJ. Having said that, BJJ competitions allow leg locks, so it is a matter of IJF rules and judgement calls.
The most important difference, in my opinion, is the emphasis in BJJ of the guard position. Thus far, all my different Judo instructors have preferred to sit up and to try chokes or turnovers (elevators) instead of going to the guard. In BJJ seminars, I have been taught that the guard can be very advantageous and it was really stressed as a desired position to be in.
BJJ is all about submissions. Get the fight to the ground and submit your opponent. Judo has submissions, but also holddowns. It values throwing you opponent as the first means of defense or attack (depending on your view) and the ground is a follow up.
These are just different approaches to the same question. In the late 1800s, early 1900s, it was Maeda, a student of Jigoro Kano, founder of Judo, who taught Carlos Gracie Judo. So ultmiately, these two arts are related.