Great question. Both get_fundamentals and the pipeline API allow you to filter your universe using fundamentals data. You are right that at the feature level the pipeline API also allows you use pricing data. It also offers is access to historical fundamentals data.
I think the real benefit of the pipeline API comes from how easy it makes combining factors and ranking and selecting your universe. You can use get_fundamentals to get various fundamentals fields, but if you want to do any calculations with the data, or use it to rank and filter a universe, you are doing the coding in pandas on your own.
The pipeline API makes combining factors and doing calculations easier, but the addition of the .rank(), .top(), .bottom() and mask functionality should make narrowing down to the securities you want to invest in much easier.
You might like this section of the documentation on pipeline, where much of this is explained.
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