See above. You are attacking a strawman at this point.
Your initial argument is "in the situation where initiative goes cleric-giant-rogue, you might be better off readying a healing spell".
The argument opposing you is "readying a healing spell comes with risks".
You appear to be trying to argue that those risks are zero. Since this is an excruciatingly difficult argument to prove, you're not succeeding.
I'm not seeing a constructed, easily defeated scenario being substituted for your own position here. In fact I'm not even seeing anyone saying that your initial argument is wrong, merely that it's a tactic that has risks.
I've only ever addressed a specific, narrow scenario.
Your scenario is specific, but in the context of D&D, nothing is really narrow.
Not sure what everyone is trying to prove by taking it out into the wider world of generic, all-encompassing possibilities. Are people white-knighting at this point?
I'm not sure what benefits people would be trying to score with Tony... and most of the defense seems to have been himself...
Or maybe trying to "school a newb" on how the rules really work?
I'm not seeing any rules arguments either. There's some argument on 'how likely is the scenario where readying an action fails?"
You appear to think that nobody ever fails a ready action.
I personally feel like readying a spell is a massive risk. You limit your mobility and risk losing your action as well as potentially the spell slot.
I think the best option in this scenario is to cast something totally different like command or sanctuary.
I might also try to persuade the DM to let me spend my action "aiding" the rogue to give the giant disadvantage on his next attack.