I’m with @Starlite on this that it’s pretty disappointing and (imo) worsens the already low value of the LT reward pool, regardless of the fact that this has been the case for a while.
Edit: to elaborate on this, I can see a case where obtaining certain Faction Legendaries would be helpful for newer players who haven’t had time to level up their Hoards and amass many Chaos Shards. However, I don’t believe newer players are the target audience for LTs or likely to be in guilds that complete them.
With the amount of Chaos Shards able to obtained from regular Delving, it is nigh on impossible for such a player to not receive at least one copy of each Faction Legendary.
The same simply cannot be said with the same degree of certainty with regards to the general pool of Legendary or Mythic troops – and I’d expect it to differ by at least a factor of 10 – in my mind, enough of a difference to warrant different treatment in LTs.
Of course, we could just, uhh… nerf Chaos Shard/Faction Legendary drop rates () enough to make them worth having in LTs.