Sorry, but the Netherlands were at the very center of the European economy from the early Middle Ages on. Most of the great cloth manufacturing centers were there. The axis of the European country was from northern Italy to the Netherlands.
The great wealth of the area was precisely why they were able to fight off the Spanish Empire, the greatest in the world at the time and supported by the looted wealth of Mexico and Peru, for 80 years.
The result of the war was partition of the Netherlands, with the still Spanish-controlled and Catholic segment (later Belgium) indeed becoming an economic backwater for a century or two. While the independent and Protestant section became the wealthiest country on earth for a time.
Charles V, under whom the rift started, was raised in the Netherlands and much more a Netherlander than a Spaniard.
As you yourself pointed out, the real rise begin with the partition of the Netherlands and Belgium and the Netherlands, as a bastion of religious liberty, greatly surpassed Belgium within a century of that partition.
The influx of Huguenots with their industry and inventiveness deserves no small part of the credit for that transformation.