Having larger photosites allows the camera to operate at a lower base ISO. Having a lower base ISO makes them better for bright light situations.

Nikon has a full frame camera with a true base ISO of 64. Most full frame cameras have a base ISO of 100. They have “deeper wells” allowing them to gather more light before saturating.

Really? Larger photosites work better in bright light and small ones are for low light? It would be nice if this were true, but it’s not.

The issue is quantum noise. You need to get enough photons to overwhelm that noise, and larger (in area, not ‘depth’) will gather more photons for the same time/aperture.

The dynamic range a sensor can capture is measured from the lowest light in which photons are not overwhelmed to full-bright.

You misunderstand the way ISO works on digital sensors, but I won’t get into that in a comment. I would suggest you head over to the DPReview Photographic Science and Technology forum and ask some questions. There’s also Google. A lot of this is basic optics/physics.