And as for as flanking goes, I do think advantage is appropriate. Go play nerf swords with a few people. Have two people attack you at once. It is SO much easier to land a hit against someone when 2 people are attacking that person. SO much easier. It is NOT easy to get behind them when soloing them.
Real people also die from the first hit or get crippled for life, but that would make for a boring game or movie so we have to bend realism a
little bit.
We can't hand out mundane ways of granting advantage without nerfing the aforementioned spells that are designed to grant it at the cost of a spell slot to oblivion.
