Now, to understand what I mean when I say "Aikido is just Jujutsu," we have to look at what Jujutsu really is as well as the origins of Aikido itself.
By it's most simple definition, Jujutsu is a blanket term for all Japanese unarmed fighting styles with an emphasis on joint manipulation, throwing techniques and grappling instead of striking. This is due to its origins as a warrior art, meant to be used on the battlefield by Samurai who for one reason or another found themselves without a weapon. As in everything, context matters. When your opponent is wearing armor, developing a sophisticated striking repertoire like Karate isn't appropriate as they are not effective.
Striking in Jujutsu is meant to change the shape and position of the body, as well as create disruptions that allow you to more easily apply your finishing technique, whether that's breaking a joint, choking them out or throwing them on their head. Styles developed during the 250-year peaceful Edo period have a greater emphasis on striking than those developed during the Sengoku period, but still not to the level that we would classify them as striking arts.
Ueshiba was awarded the Koyju Dairi (representative instructor) certificate from Takeda Sokaku in 1922. Interestingly on this certificate is where we see the first mention of "Daito Ryu Aiki Jujutsu" instead of "Daito Ryu Jujutsu." Many believe this is because Ueshiba had already begun modifying his teaching methods away from what Takeda was sharing, and Takeda did this to distance himself from Ueshiba while still keeping him under his thumb.
Eventually, due to Ueshiba's popularity, Takeda began using the name Aiki Jujutsu to describe his art as well and that's what all branches of Daito Ryu use to this day.
When you look at the technical curriculum of what Ueshiba was teaching, it all derives from the Hiden Mokuroku, which is the first catalogue of 118 techniques. To quote Aikido historian Stanley Pranin:
"Let me begin by stating categorically that the major technical influence on the development of aikido is Daito-ryu jujutsu. This art, which is said to be the continuation of a martial tradition of the Aizu Clan dating back several hundred years, was propagated in many areas of Japan during the Meiji, Taisho, and early Showa periods by the famous martial artist, Sokaku Takeda. Known equally for his martial prowess and severity of character, Takeda had used his skills in life-and-death encounters on more than one occasion. Takeda was fifty-four years old when Morihei Ueshiba first met him at the Hisada Inn in Engaru, Hokkaido in late February 1915. This encounter marked the beginning of a long, stormy yet ultimately productive association between the two, which lasted for more than twenty years."
Christopher Li of the Aikido Sangenkai has a great article on why Aikido is really just Ueshiba-Ha Daito Ryu (click here to read). Therefore, I won't go into too much detail on this subject. The video below also does a great job of demonstrating that from a technical standpoint, there really is not much difference between the two arts:
"Aiki is not a technique to fight with or defeat the enemy. It is the way to reconcile the world and make human beings one family."
There's a movement in the Aikido community to bring Aikido training into the 21st century with more practical methods that prepare the practitioner for real violence. I'm sure this is due to the pressure many are feeling from the growth of MMA and Brazilian Jiu Jitsu. Some have even thought of writing to the Aikikai to pressure them into changing how Aikido is taught and practiced. Ellis Amdur addressed that pretty concisely though (see right).
More than that, removing the spiritual aspects of Aikido removes the only thing that truly separates it from its Daito Ryu origins and other Jujutsu ryuha. We can argue about the viability of studying classical martial arts all day long, but if one is seeking a more practical approach to their training and focuses solely on the physical techniques of Aikido instead of everything else, they are simply doing Jujutsu.