Can't agree more!!!
If you look at Indian politics after independence he is the only PM who derived his power from the people directly (One of my closest friend says he is strongest leader India had have after Chandra Gupta Maurya some 2300 years ago, I agree will that but will not go for or against it here).
Before I go into details I would like to say that all leaders/politicians/PMs have something in them to reach there, supported by circumstances and conditions.
Nehru was having strongest grip on power in India. But he owed his rise to his rich and famous father and them blessing of Mohandas Gandhi. Once the state machinery was in his hands he had formidable control. He was only PM who could have managed to be dictator but he was not strongest as the country behind him was not as strong as India of Today.
Lal Bahadur Shastri was again too much dependent on Congress party. Although he proved to be strong leader but his tenure was not very long.
Indira Gandhi owed her position to being daughter of Nehru. She managed to win elections and side-step her opposition within the party and managed to have dictatorial power after imposing emergency.
Morarji Bhai Desai was PM but he was leading a faction ridden party. He was not even the boss of his own party. Same goes for Narsimharao, V P Singh, Chandra Shekhar, Devi Gauda, Gujral etc.
Rajiv Gandhi had most formidable mandate till date but again he was there not because of his talents but because of being from family of former PMs.
Manmohan Singh was proxy at the best. Sonia Gandhi was much more powerful than him and he served at her mercy.
Atal Bihari Vajpayee was there but he was too much dependent on his allies. He had to be very cautious all the time.
And then comes Narendra Modi. He rose from lowest echoleons of the society. Rising through the ranks. Understanding people at different levels. Gaining experience of governing the state before being PM, won the election for his cherishma, winning a victory which was totally his own victory. Became first non-Congress PM where party and government is under his control with popular backing by people without being son/daughter/relative of any powerful person. He is the man who has vision and necessary support to implement his vision. Thus he is the strongest leader India have in our memories or anytime after independence.