I believe there should be only one reaction — read acknowledgement (distinct from receipt confirmation, which shouldn’t exist).
I agree that there are many cases where a simple acknowledgement is all that is needed and anything else will only add writing and reading effort. Say, if I send “I am out of office today” and everyone is fine with it, anything they may say is equivalent to clicking a button that means “I’ve read and understood your message and I have no objections”.
But if they do object, no emoji gives me actionable information. Is there anything that requires my input? Do they need my bugle playing skill for someone’s birthday party? Would they just prefer me to be there but don’t have a compelling reason to force me to change my plan? None of those can be reduced to a simple “reaction”.