That may very well prove to be true, but oftentimes these types of mtx are tempting becasue they are a fast track to more powerful or sometimes end game loot. After a month in the wild most of their potential customers may no longer need that extra boost these things offer.
It's not like it only took a month in Overwatch to unlock all the coolest skins. I'm sure most players are still missing quite a few skins even now.
As these drop rates are hidden and server side, devs/pubs can tweak them on the fly to lower payouts if they feel "too many" people are getting success quickly.