E implies the ability to use additional channels at the 6 GHz frequencies. With 5 GHz there are some problems, almost everyone uses the lower ones, leading to congestion and ignoring the upper ones due to DFS (radar detection; people are not fond of their wifi randomly not working).

And contrary to yours opinion, I consider that both 4 (-n) and 5 (-ac) brought very nice things (like support for new frequencies, wider channels or multiple streams). I happened to own 3x3 MIMO ac router at the time and together with 2015 MBP, I saw what it was not necessary to provide ethernet port anymore.