I'd say that Islam's "backwardness" isn't directly because of colonialism but more because of the middle east's general decline in importantness. The Europeans started building ships capable of long ocean voyages which negated the value the Middle East had for trading with Africa, India, and the Far East.

The evolution of professional armies and gunpowder weapons wasn't followed up as quickely by the Turks whose "elite" jansinnaries were only forcibly disbanded in the mid 1800s.

These two factors caused the middle east to become poorer because trade was their primary cause of wealth and than with that lack of wealth they couldn't afford (money wise) to keep up with the technologic and organizational advances of the European powers which were soon able to project power across the seas at relative ease except for the fighting between other European powers.

The lack of wealth then of course led to a further uneven distribution of wealth and no creation of the strong middle class which brought about political, social, and ecclesstial change in Europe. Only the creation of the Suez canal and the discover of vast oil reserves and the sudden and recent demand for that oil has caused the Middle East to regain any relavance again.

As for saying that Islam has never had the chance to be unified I'd say that statement is quite the opposite. Islam started unified and then split into two major sects and that's besides little cults that appear there hasn't been much organizational change. The Turks disbanded the position of Caliph with the end of the Ottoman empire and many muslims didn't recognize the Turkish Caliph as Caliph anyhow.
Christianity on the other hand started out has a cult and had many spliter branches for the first 300 years of it's existance before it was "unified" since then it has split into Catholism and Orthodox churches with the gradual addition of new branches of christiany along the course of history and has never truly been "unified".

Yes, the "West" has caused some problems in Islamic nations in recent history but that hasn't caused the current "backwardness" we see in many Islamic nations now but really just caused those nations to keep the social status quo of when the colonial powers took over.
It took a long time for Europe to seperate church and state and hamper the power of any one church and until the middle east has the same internal revolutions I don't expect the region to change to much socially or politically.