People complain a lot about email. I understand - but it's also a modern marvel.
I see what is happening on closed systems such as LinkedIn Messages and Facebook Messages and the results are far worse than our evolving open standard from the mid/late 20th century.
So let's critique to improve the standard but start from the premise of "wow... I can't believe this works at all."
@schmudde email is infuriating until you realise its just paper that can teleport, and each reply is also just paper, and it has all the same strengths and weaknesses of letters written on paper.
which makes it immediately clear why email is so bad at being a groupchat