Granted to everything you say, but there's no evidence that what Overlord is doing now is some sort of plan B. If we're winning they should be getting weaker. But wait! They're in fact stronger than ever now. This, as you might imagine, is a bit frustrating.
We'll keep doing what we're doing because we have no other choice, but the reason people keep looking for magic solutions is that there is no obvious way to WIN. What we have here is an apparently endless fight against a mutating enemy that simply changes tactics every time we have him figured out (sorta). We kill the leaders - they come back. We destroy armies, at great cost, and a day later the same commander shows up with a brand new one.
*Edit: Seems I hit the post button too soon. Here's the rest of it.*
I have heard so many times that the Invaders have limited resources and never once have I ever seen any indication that the limits actually impose a practical restriction. The Monsters in the Fourth invasion had literally endless hordes. We must have destroyed thousands of them with the Temple of Light alone, not to mention what they threw away on some of their sieges, and they just came back every single time with a brand new army. They had so many troops that they used to drop hundreds of monsters at a time off as militia units to use *as an expendable attack force* in fortified enemy regions. The daimons and undead also never showed any sign of even approaching a limit to their forces. Anyone else remember when the daimons had 100,000 CS in a single region?
To be fair, I've seen things in this Invasion that suggest there might be some actual restrictions this time (like the army of 'Refitted Daimons' that just showed up in Sandlakes, and that bizarre little episode where three commanders recruited units of peasants), but unless these Flesheaters are Overlord's last gasp, I'm going to go ahead and say that there is no end in sight. I mean, let's say we keep on beating his armies (by no means a given) and whittle him down. Does he just... Give up eventually? Run out of armies and retreat sullenly into the Blight, ne'er to be seen again until the Sixth Invasion? If so I kinda wish that had been more clear from the beginning. I know Tom keeps yelling 'THERE'S NO MAGIC BULLET', but when things happen like what happened in Vilriil, you can't help wondering, plus in the last two Invasions there definitely were things that had to be done aside from just fending off the Invaders.