I believe this is also against Apple's Terms of Service. IIRC, they have a "most favored nation" clause which prohibits you from offering a lower price on a competing platform.
I believe they also used to have it for subscriptions to things like video services (i.e. if you offered a web price and a 'through the store' price, the store price couldn't be higher), but dropped it.
2. "You must not directly or indirectly target iOS users to use a purchasing method other than in-app purchase, and your general communications about other purchasing methods must not discourage use of in-app purchase."
I think this implies that the subscription must be the same for all devices and you can't treat iOS differently. Pretty sure having a lower price if you subscribe on Android would violate that second clause.
Right, the app must not say that subscribing outside of the app is cheaper.
Unless there is proof of the contrary, the statements you point to do not imply that a provider cannot charge a different rate on a different platform.