I agree that you should probably not jump head first into some random new framework. At least you could try it out on a side project first.
But how does Express help in this case? It is a minimalist framework that in and of itself is not enough for a mature application so you install a bunch of different dependencies and somehow make them work together.
How does that make onboarding easier when every project can have an entirely different folder structure, set of libraries, test framework etc.
Express was used merely for illustrative purposes, as it is easily recognizable. But it quite often starts from there, someone choses a framework, no matter how small footprint it has got, and then application is snowballing towards tools' mindset/guides etc.
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