Well, in all technicalities, the actual "sport" itself that is included in the Olympics is 'Gymnastics'. It is then divided into different disciplines, in this case 'Artistic', 'Rhythmic' and 'Trampoline'. Rhythmic Gymnastics are still a form of Gymnastics.
From the Olympic website
To make it onto the Olympic programme, a sport first has to be recognised: it must be administered by an International Federation which ensures that the sport's activities follow the Olympic Charter. If it is widely practised around the world and meets a number of criteria established by the IOC session, a recognised sport may be added to the Olympic programme on the recommendation of the IOC's Olympic Programme Commission.
So, following this definition, dancing (or more technically 'Dancesport') in itself is a sport (administered by the World DanceSport Federation). Even if Rhythmic Gymnastics does take influence from dance (remember, the main focus in itself is the actual execution of the Gymnastic done), that doesn't void it in any way, shape or form.
Also, tumbling is included within the Artistic Team All-Around events (male and female).
Unless you actually are fully experienced in the judging of Rhythmic Gymnastics, you can't really give an opinion on whether it's "too much about the aesthetics" or not.
In short: Yes, it's a sport. It's not a subjective matter.