Definitely, all of the early hits had a full on dance sound and a driving beat. The funky wah wah bass lines could also be seen as proto disco.
In my opinion, the song Dancing machine is pure early disco. Yet not all disco was just dance msic, some disco songs are very melodic and most of MJ's songs up to Thriller could be called disco. Most of Destiny, Off the Wall and Triumph is disco or has a strong disco feel. That is not a bad thing, because I love disco, and one of my favourite all time disco singers is Donna Summer who was the undisputed queen of disco.
In fact it is my love for disco that first got me into Michael Jackson with the disco infused hits Don't stop til you get enough and Rock with you. Disco elements exist in most 1974 to 1982 Jackson material, even smoother Philly sound jams like Let me show you the way to go and Enjoy Yourself. Dreamer has a sexy disco ballad feel along with I am Love even. Whereas Shake your Body down to the ground and Blame it on the boogie are the two most deliberately disco Jackson songs of the lot.
The fact Michael Jackson transistoned into seamless pop and rock along with some very electro funk in the Bad era and then new jack swing with Dnagerous and an almost alternative pop feel of history. Plus his dabbling with rap and even R and B auto tune with Invincible, shows how he can easily mold musical styles and trend into a mold of his own distinctly original style.
Plus a lot of disco culture and music is dancing and we all know how Michael was the greatest dancer of all time, so there we reinforce the importance of the disco sound in his music.
Proto Disco sound - Most 1969 - 1973 period (Up to Skywriter)
Early Disco (Barry white, 3 degrees type stuff) Get it together up to Goin Places (1974 -1977)
Cassic Disco - Beegees, Donna Summer, Chic etc - Albums Destiny, OFTW, Triumph (1978 -1980)
Post disco, 80s dance - Thriller, Victory,
80s Dance pop - Bad
New Jack swing - Dangerous
Melodic rap and Gfunk/Pop rap - History
R and B autotune, Techno - BODF/Invincible, songs like Blue Gangsta, Xscape etc.