Honestly i think that is only half true. The one thing I would say compared to XCOMs or Xenonauts, is that there are no land missions on alien crash sites. Which would be nice to have. But also not all games have to work the same way.
Otherwise being able to basically win the air game, and remove the air threat from the sky (which u can do at your own pace, deciding when to activate and if you want to rush or finish the air war) is in my book a positive. And despite what your comment suggest I don’t think most players would say they finish the air combat too soon. Im of the opinion that these minigames always overstay its wolcome, so being able to win the air combat, and other threads to focus on the main plot. Benefits the game for me.
It is true that it is not that well introduced (as with all other non mandatory content of the game), and is not very clear which mission activates what, or how engage with each DLC mechanics.
Still, even if you can basically not play the air combat, ot the ancient sites or use the muttons, or the augmentations, or ally with certain factions, or use vehicles, or raids, or if u can rush or activate stuf like corruption or the subject 31 subplot… I would not consider most of these side content. All those mechanics change the way the game works and are worth many hours of gameplay. The game is just designed to be non linear and different in every playtrough and in accordance to the player style as much as posible.
These mechanics are not explained very well, but the fact that players can engage with the game how they want, and at the pace they want to. Is a strength of the game, not a weakness. And the fact that u can rush certain missions and do them early if u want, is also good in my book. Even if people that rush them because they want to, later complain of being able to do it.
Still, it would be nice to have crashsite missions, or more integration with other game missions via some other way. Though I think the DLC actually improves the tactical combat a lot, and the way pandorans attack havens now is much more interesting with the DLC, which in turn makes the entire game better. Just my opinion.