Hi @mercecsp! Good question.

I'm not a camera expert, but I spent some time researching and using cameras for my short stint as a youtube hobbyist!

Also, I found this paper, which examines the effect of megapixel on perceived image quality.

I think the relevant tldr conclusion from the paper is:

For most purposes (even to view pictures on a computer), having higher MP (above 6 MP) probably won't matter much.
It only would matter if say, you want to zoom in to your images.
When choosing a smart phone camera, you'd want to look at other parameters (besides MP), like the optics (the lens), and image-processing capabilities.

(I'm not really sure about your "filter effects" point, but from what I gather, this mostly relates to image-processing. I image for most use-cases, you could just use an app, but I believe the phone's native filter options can be more sophisticated than third-party apps.)

So, it sounds like your friends are on the right track, but they should also look at the "optics" (aperture, focal length, lens quality) aspect as well!

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Relevant points from the paper – in more detail:

There is little perceived difference in quality, between a 100 MP sensor vs 6 MP sensor camera.
"Subjective quality tests demonstrated that image quality differed by less than 2 JNDs between for images from resolutions 100 MP and 6 MP"
But of course, if you want to "zoom-in", then having higher MP helps.
"... these results only apply to images displayed in full; “zooming-in” on an image would require it to be from a higher MP sensor to be acceptable."
The paper highlights three broad buckets that affect image quality. Megapixels is just one part of one bucket. The buckets:
- (i) "sensor parameters" (which includes megapixels, noise, etc)
- (ii) "optics" (which I believe are lens-related parameters like aperture, focal length)
- (iii) "image signal processing" (which I believe mostly relates to software)
  "Although it is well established that, increasing camera MP resolution contributes, generally, to sharper displayed images, it is well known to camera experts that optics, other sensor parameters (notably noise) and camera image signal processing (ISP, e.g. de-noising, sharpening) also affect considerably both resolution and sharpness."

Camera Specifications on Smartphones having 200MP. Will we even know the difference?