Is it all about megapixels?

We all upload out images to social media accounts like Instagram, Facebook and Twitter. Each one uses compression algorithms to make your images smaller so that they take up less space on their servers and so that they load quickly into your browser/mobile. 

I wanted to see if shooting with 3 professional cameras and a mobile phone made much difference when uploading to the internet, and persuaded my wife to take part in the 'quiz'.

Here are the cameras and lenses:

1. Canon 5DSR with the 100mm Zeiss Makro-planar f/2.0 at 51 megapixels

2. Sony A7Sii with the 100mm Zeiss Makro-planar f/2.0 at 12 megapixels

3. Fujifilm GFX50s with the 120mm GF f/4.0 at 51.4 effective megapixels

4. My Samsung Galaxy Note 8 shooting in JPEG mode only at 7.9 megapixels

I went through the exact same workflow for each image for the black and white conversion and for some gentle skin softening. That's it. 
All images were then converted from RAW to jpeg (apart from the Samsung which was already jpeg). Answer like this: A2, B1 etc... how will you do?