Acctions are a core feature of OH and very commonly used by all levels of users. I doubt you would find many who do not use Actions.
From an end user perspective, a rule Action is the best of the three.
It’s even possible to create a custom Block library to make the Action available in Blockly (e.g. here’s Telegram’s Block Library: Telegram Actions).
There have been some recent changes to to MainUI to make them more accessable from siimple UI rules too so one doesn’t even need Blockly code to invoke them.
You should have no reservations about implementing this as an Action.
Have another Channel with a Switch Item to command to send the message all at once.