Yes, you are correct the leadership is not guaranteed forever, but given apple's track record and their unique positioning in the market, I am certain they are sorted for at least our lifetime and likely a few decades beyond that.
The weak point of apple is they don't make their own chips, they rely on ARM for the core design IP and TSMC for manufacturing, whereas samsung I think has their chip design and manufacturing in house, despite that they aren't the leader.
Which tells that apple's focus on optimization and strategic partnerships seems to be the winning formula for now, but for how long? I say at least few decades.