App cut is taken at the time of purchase not at time of donation or withdrawal. So on iOS it costs 30% more to buy a coin precisely because they give a cut to Apple. But once the coin is in the system, the cut has been paid and gifts do not have an additional 30% cut.
Also people compare this to twitch, but for twitch's own gifting system(Bits), streamers get 100% of the bits when they cash out. the 50/50 split for the subscriptions(when a viewer subscribe to a streamer - 3 tiers, the cheapest being $4.99)
