Strong product brands aren’t better than weak ones in every situation and brand architecture.
Samples within the automotive area may illustrate the differences.
A VW-driver will always tell you, what model she is driving. And only the model. The umbrella brand VW (or „Volkswagen“) is not announced.
There are some reasons for this behaviour:
Volkswagen is a long word. It’s generic in German (Car for all people). For some German ears it’s a nazi-word („Volk“). So the people turn to „VW“ instead. The company itself does us Volkswagen (for the umbrella enterprise, to which also Audi, Skoda and many other brands belong) and also VW (as the umbrella brand for the VW-Line within the enterprise).
There are many very different models under the umbrella brand: From luxurious sedans (Phaeton) to real small cars (UP in Europe, a car smaller than a Golf).
The product brands are nice to use and to pronounce and they can separate the different model lines within VW and – also – separate them within car models wordwide. That’s fine.
Different: BMW brand and product line architecure
If a BMW-driver is asked what sort of car he rides his answer will content the umbrella brand. That strengthens the umbrella brand but the other reason why the brand BMW is stronger than VW is that the model series are branded „only“ with 1,2,3 etc. They are much weaker than the VW product lines.