I will say this as a shia. Banish your varna system nonsense. It is the reason why your nation was so easy to subjugate and rule.And how is hinduism montheistic? Sikhs who are half-hindu,half-islam,Arya samajis,Brahmo samajis are monotheist. Hinduism is a syncretism of several traditions.
They came about due to common sense and if they have failed in this environment,they ll go due to common sense again.
I feel your idea and analysis of this system is very external and not complete.
I guess you don't know that,there are reservations in education and jobs for all the classes who were weaker.
Nonetheless,these things have nothing to do with the invasion,there was a whole different reason for that.
Sikhs are hundred percent similar to Hindus with slight differences and they have nothing to do with Islam.
Hindus go to Gurudwara and Sikhs go to temples,unlike Muslims who go to neither,we have no such prejudice,we even go to churches and zoroastrian temples whatever.
Monotheism/POolytheism are mere words,it matters to muslims/christians too much and they keep harping on it whereas the original monotheists the jewish people dont want to convert anyone to judaism because they dont have silly politicial agendas.
This is like how many sunni muslims say that Shias/Ahmedis are not muslims.
You should not analyse this from your point of view,with your structures,just be informed of our things from us.
we do not need any kind of spiritual/political structures from Sunnis/Shias.