I don't know about that. The stadholder didn't have that much power. He wasn't a king (although they often tried to be one). The political power in the Netherlands was at the rich merchants in Holland. They had the power and controlled the Netherlands. Ok, as I said the stadholders often tried to gain the power of a king, (Dutch political history of the 17th and 18th century bascly is the strugle of stadholders against the merchants) but in the end they always lost (which is why there were two stadholderless ages).
In this scenario the stadholders have even less power, certainly considering Willem IV and V, who were stadholder over all provinces. The stadholders would not fight amongst themselves. First of all Gelderland, Overijsel, Groningen, Friesland and even Zeeland and Utrecht weren't important. The power in the Netherlands lied in the province of Holland. The merchants of Holland ruled the Netherlands. The stadholder of Holland was the most (perhaps even the only) important. That is why for more than a century there were two stadholders in the Netherlands, the Frisian ones and the stadholder of the other provinces. They never came into conflict, because only the stadholder of Holland was important. That will be the same in this scenario with three stadholders.
Actually I think this system is far more stable than one stadholder for the provinces. Because the stadholder of Holland will have far less influence in the other provinces, so he won't be able to challenge the merchants as effectively, so they remain in power, creating a far more stable situation than the constant power struggle.