Max cargo weight for Gazelle HeavyDutyNL
The limiting factor when it comes to durability and cargo on a “normal“ bicycle are the wheels. The Ryde Zac 19 rims used on this bike actually list
“MAX. SYSTEM WEIGHT (KG): 110” in the specifications. They also don’t recommend it for “HIGH LOAD 130KG” usage. Though that seems to be a rather conservative estimate considering the weight, number of spoke holes and symmetrical rear wheel (possible because of the internal gear hub).

I think the 135kg limit is reasonable.

I think in daily usage the bad center of gravity of the cargo will be a much bigger problem than a lack of durability. The cargo is sitting very high and the middle of the rear rack is behind the rear axle. If you are loading the rear rack only the whole bike will tend to rear up.

So even if the bike had stronger wheels (e.g. tandem wheels) it would be quite unwieldy. At some point overheating of the brakes and lack of very low-speed gearing could become an issue.

To me it seems to be a very heavy bike without any real advantages. Other bikes like the Surly Long Haul Trucker can do the same at “just” 15kg of weight.

If you want to transport more cargo get a real cargo bike or a trailer.