I'd honestly prefer them to keep the 'specialist' troops to event buildings like the Orc Strat Grounds & V.Valors - that way you can access those troops well before the chapters in which they unlock, AND, "soon" with bp's/rr spell upgrade them as you progress through the game.
No reason both can't exist, as any new AWs are going to be obtained at a point long after you can produce these units normally. As well, I personally don't think those event buildings are very good unless you're so early in the game that you haven't even unlocked units of that type at all. Orc Strategists are better than nothing, but if you have your Mortars or Golems unlocked you can get by just fine with those, and same deal with Paladins/Treants in relation to VGs. They're not very effective for anything even though they're free because the output is so low. I could collect up to 480 Orc Strategists per day from an event building at my level, or I could train 21,650 per day in my Training Grounds. While the free Strategists are appreciated in the relatively small footprint, overall they're a drop in the bucket and they aren't worth chasing down in events compared to the much more useful troop boost buildings if you're looking to fight. AWs on the other hand, while still not matching the output of the actual training buildings, have much higher returns (currently collect about 4 free squads per day from each of mine) and don't require diverting resources like event currency (which as mentioned, I consider better spent on other things) in order to acquire them. They do have heavy costs in other areas, with arguably the steepest of which being mandatory tech progress.
Anyway, perhaps it's just perspective. I see little value in obtaining units 'early' from event buildings since you unlock all of the unit types early as it is and they're enough to get you through. The other tradeoffs for that one small benefit (event currency/availability requirement, low output, do not scale at all with your squad size) just make them seem very unappealing.