You are absolutely wrong!
As I said again, the RA will be a crucial part in the alliance against the World Government. If you believe the "fodders" won't participate in that war - for whatever reasons you may believe... - there would be no point in drawing the reactions of all the fodder pirates, civilians, all the people in those islands which the strawhats even sailed before.
Remember before Wano when everyone was hyping up the Wano Samurai and their huge army? That's you right now. Yes, there'll be some fodder fights going on in the background. That's what the Grand Fleet is for. But it's not going to be Kingdom. You know the focus is going to be the strong characters and groups that have already been set up.
The point of drawing reaction from all the "fodder" is that these are the actual characters we've met throughout the series. Oda wants to tell their story as civilians experiencing this global disaster. If it was about civilian recruitment, he wouldn't be focusing on characters like Kaya and Tonjit, would he?
Nobody is stating these characters will face stronger forces of the WG but this speech is supposed to set things in motion, to "shock the world" - the incident in Egghead Island is supposed to shock the world as I said before.
So yes, it's most likely islands like Water 7, Alabasta, Dressrosa, etc. will join the armies or at least they'll be equipped to be prepared for the upcoming war because they'll know the WG is on their asses. You cannot fight an enemy unrecognisable for you.
Again, why do you go from "shock the world" to "fight the WG?" The world flooding is shocking enough. It sets things in motion enough, like I laid out.
There is a worldwide broadcast of the most smartest scientist in this manga and the population will only find out later that the obvious evil is responsible for all their misery - the reason why they need to get in a boat and get to higher ground, to the mountains, etc. - and then they'll keep on praying for Luffy like it's no tomorrow?
I believe they will all have their own individual stories of surviving this. They don't necessarliy have to tie into the grand narrative. So e.g. next time Nojiko won't want to leave the orchard, after that Genzo will be leading everyone to Reverse Mountain, after that they meet Crocus and they all talk about Luffy etc.
Where it all comes together is when they, you know, come together. In Water 7. If one city contains just about every character in the first half of the series, and the WG are about to nuke it for that very reason, that's a pretty big story beat don't you think? Much more dramatic to me than generic "final war", "big crowd vs. big crowd" etc.
Again, another reason why the broadcast is pointless. All the higher ups are already set in motion ever since Doflamingo got defeated.
This speech isn't only important for all the big players but also for the weak and so far, this speech doesn't even explain the cause for the world sinking. Heck, the WG could EASILY draw their own narrative and point the pirates, especially the strawhats, as the devils who want to bring harm to the world. You ever thought about that?
It turns the "throne war" from a cold war to a hot war, because now it's a race against time. It also recenters the conflict not just on getting the One Piece, but on gaining control the ancient weapons, controlling the high ground etc. It absolutely sets the stage way more than Doffy going down did.
And yes actually, that'd be good storytelling if Luffy was made out to be the devil. It'd put all his friendships in the series in a direct test against a worldwide propaganda machine.