If it doesn't affect the narrative, then I don't care about in game purchases. I've always maintained that if people want to buy things to make it easier, let them. To me, its essentially the same as purchasing an action replay disk for a console game years ago.
If you are required to purchase something in order to proceed, or to get the true ending of a game (DLC expansions not included where applicable) then there is no place for transactions.
In the case of Shadow of War, the loot boxes are designed... See More
to give you an extra orc or two for your army, as well as consumables that have effects such as increased damage, increased exp gain etc. All they do is make the game progress a little quicker, make it a little easier.