eh, they're not necessary at all.
Unfortunately, "not being necessary" doesn't mean they don't have an impact. If the game is made even +1% grindier due to the presence of de-grind / pay2levelup / "TimeSaver" MT's (as they absolutely are being designed around MT's in advance), then that's still a major problem that affects even those who don't buy them.
"You can buy Helix Credits to spend on specific cosmetics for you or your mount, legendary weapons, and "Time Saver" items and map markers. Those Time Savers include in-game money, as well as crafting materials for upgrading and skill points for unlocking new abilities. You can also pay $2 each to automatically reveal the locations of the certain secrets, including Ancient Tombs, Hermit Locations, and Stone Circles."
http://uk.ign.com/articles/2017/10/...microtransactions-everything-you-need-to-know
Question : What's the difference between me "Time Saving" by buying these MT's, and me "Time Saving" for free by using Cheat Engine to 'gift' myself the exact equivalent of money, crafting materials, skill points and "unlock secrets" cheats before using a save-game editor to 'gift' myself the same Legendary Weapons, whilst demanding others who want to compare Achievements acknowledge that I haven't really cheated, just "alternative time-saved"...
Like shortylickens, I won't be buying AC:O either as it clearly isn't just cosmetics. It's glorified pay2cheat for the same stuff that "AddGold 10000", "GiveSkillPoints 20", "Summon Nirnroot 50" or "idbeholda" cheat codes did for free across +20 years of older games, (except that those older games didn't have 'fake-grind' artificial game-time padding that affected even those who didn't use them). To many, it's this "obvious fake grind" designed solely to act as in-game adverts for MT's that makes the game (and developer) trashy as hell.