Originally Posted by Child-of-the-Emperor
Well, if we also use the Word Bearers series which claims that the Black Legion outnumbers the Word Bearers as much as 10:1, as well as more mainstream lore such as Codex: Chaos Space Marines, which states that "with every assault Abaddon leads, the strength of his Black Legion grows", it is not unreasonable to assume that the Black Legion (as a coalition of warbands) far outstrips the Luna Wolves/Sons of Horus Legion at its peak.
I don't think the BL could outnumber the WBs 10:1 in Astartes. That would be insane.
The WB's forces are made up of "hosts". We know that a host is anywhere between 1000 and 3000 men. From page 543 of the WB omnibus:
"From the number of ships we are reading, I would hazard that there are around five or six Word Bearers Hosts bearing down on Boros..."
"If that is true, we may be facing anywhere between five and fifteen thousand Word Brother zealots."
I would assume the average number per a host is 2000.
We know that 45 hosts exist as an absolute minimum. From Dark Creed
"More than twenty hosts have joined the Brotherhood. Dozens more will join before Erebus has any idea of the danger he is in."
That's assuming "dozens" means exactly 2 dozen and "more than twenty" meaning 21. And apparently that's not the whole of the WBs either, since that's only as many would have been swayed before Erebus would have discovered the plot against him.
So the extreme low estimate would be 45,000 WBs in existence (45 hosts at 1000 Space Marines each). This assumes that every other host, including Erebus's, would be swayed before he realized it, not likely given Erebus's flair for intrigue. And that by "2 dozen" it would strictly mean only 24 more hosts would join them. And the absolute minimum for the host size would, in fact, be the average size.
A middling estimate would say around 105,000 WBs (say 50 hosts in the Brotherhood, 20 not part of the Brotherhood and each Host made up of 1500 men).
A high end estimate would be around 220,000 WBs. Around 80 hosts in the Brotherhood, 30 not in it. 2000 space Marines per a Host. (Note "dozens" means 5 in this case.)
To outnumber the WBs in terms of Astartes 10:1 would probably mean the BL has 400,000 to a million Space Marines. Though a couple million would not be entirely out of the question.
That might fit with the idea that Abby has more Space Marines than Horus ever did, but it doesn't quite fit in the lore. With a million Space Marines he could steam roll through the Imperium. All the Black Crusades would be the barest skirmishes compared to the forces he could bring to bear.
Originally Posted by Child-of-the-Emperor
I can't fully remember the context of that claim, but take into account that Talos is bitter about the use of Chaos and daemons, viewing the Black Legion as weak for collaborating with Chaos. Perhaps it was a misguided claim as a result.
In fact, it seems to be assured that Talos was misguided in claiming that the Black Legion had withered, seeing as though all other established lore claims that the Black Legion has only grown in strength and numbers since Abaddon's rise as Warmaster.
I don't think it was a bitter claim. Abaddon was argued into a corner. It's on page 168 of the paperback.
"After centuries of defeat, after failed Black Crusades, after infighting and war has bled your Legion dry, and draped you in ognominy among the other Legions? Is it not true that your men are slaved to daemons to make up for the great losses you have sustained since the death of your primarch? You leech strength from other sources, because your own Legion's might is almost gone."
Silence answered this proclamation.
Abaddon might have laughed. It would have been the act of a great leader to laugh, to humour a lesser warrior, to bring him around to his own way of thinking through persuasion and empathy--even were it all false. But Abaddon was not such a leader. He was shrewd enough, at least, to guess Talos would never be fooled
I reconcile the difference between Abaddon controlling more than Horus ever did and Talos's statement by saying that, yes, Abaddon's forces are greater, but not in terms of Astartes. Abaddon may have more renegades serve under him, more cultists, more traitor Guard, and other forces (like daemons). As a whole these forces eclipse what Horus had. I would like to think, Space Marine to Space Marine, that Horus had more.