I would tend to agree with this. Zakat was not enforced at the time of Prophet Muhammad. If we look at the situation back then, it was probably never needed to be enforced since the Sahahbas usually would fully obey by the order of Muhammad (PBUH). There was not need to enforce such a thing strictly.
After The Prophet (PBUH) died, people started a revolt and refused to pay Zakat. Abu Bakr (RA) fought against these people and collected Zakat by force. Excerpt from this link
The second major problem faced by Hadrat Abu Bakr Siddiq ra was that
many people refused to pay the Zakat, which was essential for fulfilling the needs of the Islamic state and caring of the poor.
Hadrat Abu Bakr ra vowed to collect Zakat from every one and took
all the necessary measures to achieve this goal.
This link (Shia view) says that the first two caliphs took Zakat revenue using tax collectors. This means it was made compulsory at the time of first two caliphs. There was no option of not taking it. This article also says, Ali (RA) also took Zakat by force but he introduced some leniency in it. That is people may choose not to pay.
I think it obvious from the links that everyone paid Zakat at the time of the prophet so there was not need of enforcing it. But after the prophet (PBUH), people did not want to pay Zakat as their Iman weakend. The caliphs did the right decision to take Zakat for force.
In my opinion, Zakat was always enforced in Islam. We have proof that the first four caliphs collected Zakat as tax so Tax is Zakat. You do not need to pay Zakat and Tax separate.
Islam does not put extra burden on people. There is no need to pay Zakat and Tax separate. If you have paid 2500 tax, and you own 3000 Zakat, you can simply pay 500 as Zakat and you are all set.