It’s DLC, so almost by definition it’s side content in that you don’t actually need it to complete the game.
Personally, I agree with all the criticisms and have told the devs so on many occasions in so many words. Paradoxically, LotA is too resource-intensive for what you get - but what you get seriously unbalances the game.
It’s also a massive plot Spoiler if you engage with it too early. It’s better than it used to be - because the devs at least took advice and delayed the trigger until Symes’ Grandfather is introduced - but it still assumes you know about the Antediluvian Civ before you’ve learned what this is from the main story thread.
So my advice in Phoenix point: some helpful hints for xcom players is not to engage with LotA when it first appears.
The way I and some others I know in the Council play it, we view it as optional side content to engage with during the endgame while you’re waiting for the Story Research to mature. This way, it gives you something to do with Squads that are actually strong enough to do it, and adds to your arsenal at a point where the Pandas are at their strongest, so it doesn’t feel too OP.
That said: I don’t like it very much and ignore it most of the time. I rarely agree with noStas, but in this case I think (s)he’s right.
I’m hoping that Festering Skies will be much better thought-out.