Taking this a step further with the flex/main support spectrum. This conversation always confuses people bc there are outliers where metas include double ms/fs.
For any combo, the flex supp will play the left hero, the main supp will play the right hero, with few exceptions.
Some people seemed confused about who is Flex support and who Main support so here is the actual non meme version. The roles have nothing to do with healing amounts it's based on esports. Main support player learns the few core heroes that are basically always played. Flex learns everything else.