It’s more about the lack of iMessage features. Things like editing, unsend, text effects, etc are absent in regular texts. If everyone is on iMessage, everyone can use those enhanced features. They’re apparently pretty popular in group chats, but even a single android user will drag the entire conversation into regular text messages instead. So lots of iPhone users (especially the younger gen Z and alpha) started complaining whenever someone had an android, or even outright bullying them for it.
And for android users, texting with an iPhone user is a horrible experience; Images are horribly compressed, videos are severely limited in file size and compressed, group texts need to be opened as an attachment to be read, etc… All because iOS refused to use the more modern RCS texting protocols.
That’s more on the OS than the text protocol. The protocol doesn’t just hold a text in the ether until it’s time for delivery. A scheduled text is you telling the phone “hey, wait to send this message until it’s time.” Then your phone sends it at the proper time.
iOS still doesn’t have built in text scheduling. There are workarounds, (like using the Shortcuts app to build a “send this text” automation that runs at a specific time), but that’s not the same thing as native support.