Sorry friends, I could not get time to contribute something meaningful till now. Here is my piece on the subject.
Classification of anything must have some basis-religious, social, linguistic or simply geographical. When we use term 'Deccan', this is our classification of a certain region in India. As per even ancient Indian scholars, the Aryavarta stopped at Vindhya and Vindhya mountain as well as Narmada river indeed maintain a barrier between regions north and south of them. Now, Sanskrit Dakshina meaning South was called Dakkhin (rural people still use it) in vernaculars of North which were taken there so Deccan has ultimate origin in Sanskrit term Dakshinpatha. However, not all lands south of Vindhyas are called part of Deccan, Deccan means lands between two seas and between Mysore plateau and Vindhya roughly including Maharashtra, Telangana , Andhra and Karnataka. Deccan does not include Tamil Nadu and Kerala.
Deccan region is relatively drier but in Maharashtra and Karnataka due to land being blessed with fertile black soil(suitable for cotton and nuts) and semi arid lands requiring far more organisation of human resources, some very strong empires were built in Deccan and since 3rd century BC, Deccan region has been an urbanised place at a time when Punjab and Rajasthan did not have much cities.
Deccan based Satvahana empire. Capital was in Pratisthan near modern day Aurangabad of Maharashtra.
After Satvahans, we have series of some very strong empires which were made by Kannada people from North Karnataka of modern day Bidar, Gulbarga, Bijapur(all three great cities of 'cosmopolitan' Deccani Sultanate) region who by combining adjoining areas of Maharashtra ruled a far larger territory than most kingdoms of India of that time.
Chalukyas of Badami( Bagalkot in Karnataka) created a strong empire which ruled over Maharashtra, Karnataka and much of Andhra. Pulakesin also repulsed invasion of Harshavardhana. Chalukya dynasty at its height in seventh century.
Chalukyas were overthrown by Rashtrakutas (ethnogenesis of Rathores is work of them only) in 750s and Rashtrakutas were indeed most powerful dynasty produced by Deccan before age of Marathas. Arabs who knew all major regions of Eurasia themselves admitted that Rashtrakutas were one of four most powerful and greatest of Kings of entire world(Arab Abbasids, Tang Chinese, Byzantines and Rashtrakutas were four such kingdoms) of 9th century. It is testimony to strength of Rashtrakutas that King of Sri Lanka offered them tribute and their armies sacked great city of Kannauj three times while Pratiharas their arch enemies could not even cross Narmada river in retaliation.
This is the reason why I said that it is indeed sad to note that Hindus of Deccan who produced one of greatest of kingdoms of ninth century were not able to reach good positions in Deccani Muslim Sultanate but an Ethiopian from some thousands of miles could become chief if he was a Muslim.
In last quarter of tenth century , Rashtrakutas were replaced by Chalukyas of Kalyani (Bidar in karnataka) whose greatest extent was same as Chalukyas of Vatapi. When Muslims attacked Deccan in around 1300 for first time, they faced three large kingdoms-Hoysalas, Yadavas and Kakatiyas. All three of them were feudatories of Chalukyan empire till 1150s.
