No, no, no. Historical games should NOT be focused on unit roster updates and individual leaders ("legendary lords"
WTF). It doesn't work for historical titles, as we're all about to find out with TW:3K and MOBA themed "hero packs." Faction Packs don't make good historical content either, unless it would be adding something VERY substantial, like India to the TWR2 map.
What makes good historical content are gameplay systems of economy, diplomacy, politics, war, new campaigns like Charlemagne that reuse assets, and new maps and cities to fight over. Some of this is similar to what Paradox does with EUIV updates and what we saw for the first time with the political and family tree updates to TWR2. If instead of these kind of updates, CA focused on bringing new factions and units it would be incredibly dull to play. It would also encourage them to leave more and more out of the game and resrict mods. Mods can do skins and units, etc. Mods can't put a political system or a walled Jersulaem, or a new campaign map. Mods can't create a family tree mechanic.
Warhammer is singularly focused on models and units and how they interact in battle. I see the popularity of Warhammer DLC by its community as a genuine threat to what Total War is. It would be a huge mistake, which you in essence are making, to extrapolate WH fantasy things to historical titles. I fear CA may be doing just that with 3K.
Alternatively, instead of faction and hero packs, CA could decide to strip or postpone historical games of their mechanics up front, and add them back in over time with paid DLC. The point here is really like a games-as-service model, to dribble content out and keep the fanbase wanting more, a Pavlovian response for frequent "updates" of content. This could be the coming reality, and every nerdgasm or nerd rage Warhammer fans make over "high quality faction DLC" only encourages CA/SEGA to fundamentally change it's game design and development practics.
So like I've said before, Warhammer really represents a mortal threat to continued positive evolution of historical Total War, as it exemplifies further dumbing down, to focus on faction mechanics, unit variety, and heroes, streamlining and dribbling content and getting fans to salivate about the next update that's just around the corner.