You've said If Islam is properly applied, there would not be any meddling and Zakat would be applied appropriately. I guess you have more faith than I do that a human vested with these large sums will apply it appropriately. Humans can be greedy, corrupt, and clumsy and may not practice the word of the Quran accurately. They could simply make bad mistakes, without any bad will. Having centralized access to large sums of alms could result in Zakat going to benefit other powerful parties as well. Since it is collected by government, it would be hard for those paying it to stop payment in protest if someone did start meddling. Note this is also a problem with secular welfare systems, I am not saying it is a problem only with centralized Zakat.
>It has been historically documented that in Iraq during Ummayad rule, there were no more poor people left to accept Zakat.
Umayyad had a variety of religions of persons overseen by their caliphate. Was Zakat distributed to poor Christians in the Caliphate? Or did Zakat only go to Muslims? This is important to know, because supporting only minority of the poor who practice Islam could mean Zakat may have not solved poverty for the entire populace. I'd also be interested in seeing the citation that poverty didn't exist under this caliphate.
In America we have the problem that lots of administrators and bureaucrats siphon off much of the money in the welfare system into their salaries as well as issues with the money going into the hands it is intended to go to. Also since the money is taken by force, there's not a lot of control by those who contribute the money over making sure it is used appropriately.
I will note I find it both fascinating and worthy of respect that many cultures have come up with their own ways of helping the poor.
Personally I would be much more on board with a decentralized type of Zakat where individuals can pick what charity to go to, in order to protect from centralized failures of government.
>I meant how would inflation happen in case of Zakat being enforced? They're orthogonal things unless I'm misunderstanding you.
If I wanted to enforce Zakat via inflation, I would mandate people to hold their money in bank, as debt, or fiat denominated bonds, and then I would inflate the money supply by 2.5% by mailing out 2.5% of the current supply to the poor per year, or something approximating that. But that would also be an imperfect system.