Re change in Jinnah after 1920
One cause of change in Jinnah was probably  British government's allocation of Central Legislative Assembly 
seats in the 1919 Montford reforms for India.
In 1909 Muslims were allotted 5 of 27 elected seats, according to Ambedkar's book. (Wolpert says 8 of 28 nonofficial seats).
In 1919 Muslims were alloted 52 of 104 elected seats, ie 50%.
So Muslim politicians went from being a minority of the elected Indians  in the Central Assembly to equal in number 
to the other Indians elected.
From Ambedkar's Pakistan or the Partition of India:
Central Assembly seats
1909
Nominated + exofficio = 41
Elected General	      = 22
Elected Muslims             = 5 (Wolpert quotes this number as being 8 of 28 non-official)	
Total 		              =  68
1919
Elected General =	52
Elected Muslims =	52
Nominated members =	41
Total	               145
Percentage of Muslims to total population was approx 24%
The proportion of seats to total granted to elected Muslims in 1919 was 36%  with elected non-Muslims also at 36%. 
In short, between 1909 to 1919, Muslims moved to centre-stage as bulwarks of the official/nominated bloc in the Central 
Assembly. A Muslim politician would get the signal that would be more worthwhile to advocate to the British 
than to other nationalists.
Incidentally, in the 1935 Government of India Act, the proportions granted in the Central Assembly were not very different:
General+SC	105   (SC=19, General=86)
Muslim 	   	82
Others		63    (Sikhs 6, Christians 8, AngloIndian 4, Europeans 8, Landlords 7,labour 10, industry 11,women 9)
Total		       250
http://www.columbia.edu/itc/mealac/prit ... /411a.html
http://www.columbia.edu/itc/mealac/prit ... /411b.html
http://www.columbia.edu/itc/mealac/prit ... 15app.html
Those provincial assemblies  elected in 1937 which had elected Hindu majorities, Jinnah and Muslim League rejected within 3 months.
IOW, unless I am mistaken, Jinnah the great nationalist never in his lifetime had to accept the legitimacy of an elected Hindu majority government(ie government responsible to an elected Hindu majority legislature) whether in the provinces or at the centre.