I don't think it is specious. Email == electronic mail, if someone sent you a letter you'd not send a reaction back, you'd sent a reply letter. But companies have been trying for years to make email more like a chat app. Threads come to mind. I I prefer folders over tags too.
Sorry, no. You’re trying to carve out some special use case for email as if it’s primary use is formal communication. Email is used for everything from formal business communication to friendly chats to fwd:fwd:fwd: Grandma’s chain letters.
On the other side, text messages are essentially just small emails and your argument against “reactions” applies equally.
We'll have to agree to disagree. For me, and the way I use these things, emails are formal, text/chat is informal. I've never and will never use email like a chat.
If someone was attempting to use email as such with me, they'd likely be getting no reaction at all.