Is artificial lighting really better than natural sunlight for plant growth?

I was browsing plants at a fish store today and was told that I needed a special aquarium light designed for plants to maintain about half the options there. That makes sense, as plants need light for growth, but when I mentioned that the tank will have access to natural sunlight, the worker told me that it was irrelevant.

I know that excessive light exposure can lead to issues like algae in the tank, but is the point of aquarium lights not to mimic natural sunlight? Does plant growth really rely that heavily on the artificial lighting you purchase?

To note, my tank (which is still being set up) is not directly in front of a window. It’s in the corner of my room against two walls, with one width of a tank facing outwards next to a window that allows a decent amount of sunlight in during the day.