Warning: Long ramble on history inbound.
Modifying koryu ju jitsu, he created a new system.
I think it would be accurate to state that he:
1. aggregated the available techniques and information,
2. culled techniques that could not be trained "alive", (arguable, I know, as Kano kept records of all of the techniques to preserve the styles, but given that this was all sealed away I think it's a fair statement)
3. created a curriculum for learning,
4. formulated an overall "game plan" (obviously while kuzushi wasn't his idea, with traces being found in Kito-Ryu, I think his systematic approach justifies being called a separate thing)
5. created a competition ruleset to promote values they thought important, and
6. promoted a method of training ("alive") that led to skill acquisition (obviously he wasn't the first person to train on a live resisting opponent, as Sumo had been in existence for many centuries).
As a result of these actions, and with the help of other full time grapplers, the environment/methodology and competition goals he created drove innovation. Ironically, it drove innovation that he himself would come to disdain (see: extended ground grappling), as he felt it was not effective for self-defense.
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As for the Gracies, beginning with Maeda's view point (which differed from, I think we can agree, from the message of the Kodokan), they:
1. aggregated the available techniques and information (many gracies cross trained in wrestling, sambo, luta livre, catch/shooto/whatever the hell you want to call it, and other grappling arts; I think I recall one of the early non-brazilian black belts saying he learned of the "omoplata" from a lethwei tournament. Ignoring that, they also had some striking elements (that lame-side kick to close the distance, kicking to stand up in base, striking on the ground, etc.))
2. culled techniques (albeit not in the same manner as Judo, but more so those that did not fit into the methodology/risk tolerance of the Gracies)
3. created a curriculum for learning,
4. formulated an overall "game plan" (regardless as to one's opinion of their game plan, it was certainly different from that of Judo. I'm sure some would make the argument that Fusen Ryu / Kosen had the idea first, but A) there's a lot of misunderstanding regarding Fusen Ryu, and the overall preference for ground fighting appears to be Tanabe's preference as opposed to the stylistic preference, and B) Maeda was about as far geographically as one could get from the epicenter of Kosen Judo, and more importantly, left Japan before "Kosen" became a thing. It's similar, sure, but it's not a direct derivative. If we're playing the "who thought of it first" game, we need to name it after some Greek wrestlers)
5. created a competition ruleset to promote the values they thought important, and
6. promoted a method of training ("alive") that led to skill acquisition
As a result of these actions, and with the help of other full time grapplers, the environment/methodology and competition goals they promoted drove innovation. Ironically, it drove innovation that they themselves would come to disdain (see: berimbolos/modern BJJ), as they felt it was not effective for self-defense.
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So, given that they by and large took identical steps in formation, either both Judo and BJJ are "new" enough to be considered their own arts, or if BJJ doesn't "innovate" enough, then neither does Judo. In which case Judo should just be called Japanese Jiu Jitsu, but then arguably BJJ, as its derivative, would retain its same name.
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I think a strong argument for the moral rights of BJJ could be made that it should be called "Maeda Jiu Jitsu," since he likely was the originator of these ideas amongst the Gracies (which gets even more complicated, because how do you ignore Geo Omori Jacyntho Ferro, Donato Pires dos Reis, Takeo Yano, Sumiyuki Kotani, and Chugo Sato). But the Gracie marketing team was strong (which borrowed from Maeda's marketing style, but neither here nor there), and here we are.
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Arguments aside, and as a practical matter, the term "Judo" wasn't mandated by the Japanese government until 1925, and the term didn't become widely known in Brazil until the 1950's. To think about it in today's modern context though, it's an atrocious idea to name it after the prescribed by "common knowledge" of the average person. It would be akin to an American learning BJJ, changing it, and calling it something like "American Karate." Awful. Though I guess we've kind of done that with "Submission Wrestling," eh?
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On a parting, random thought, I have read some speculation that Maeda's use of the term "Jiu Jitsu" was intentional. No one within the Kodokan referred to Judo as "Kano Jiu Jitsu" (historically, you can only find one item that calls it "Kano Jiu Jitsu," and that's a book written by a European, filled with non-Judo, but used Kano's name to boost sales. For better or worse, the site "Global Training Report," which is popular for its rather critical approach to the Gracie family and BJJ in general, relies heavily upon the information in this book to influence their opinion on the history and originality of BJJ. How they rectify this in light of the fact Kano signed this book for a person writing, "This is not Judo," I don't know.). It was instead Judo. So why would Maeda have called what he did "Jiu Jitsu" instead? The obvious answer, as I said before, is public recognition. Same reason Tae Kwon Do schools advertised as Karate in the 90's/00's/(now). But another interesting perspective is that Maeda didn't want to call what he did "Judo," as using Judo in free fighting was a sure fire way to get on Kano's shitlist. Put another way, Maeda differentiated between free fighting (Jiu Jitsu) and a method of physical, mental, and psychological development (Judo). But again, that's just speculation.
