It's true that iPad sales seem to have reached saturation point, but competing tablets aren't making any more significant headway either. It's peaking as a market segment, but it's a segment still thoroughly dominated by the iPad.
iTunes sales are also peaking because streaming is taking over. It's too early to say how well Apple Music is doing, but there's no indication it's in trouble.
Apple Watch has significantly expanded the smart watch market and taken over 75% of it. What is that supposed to be lagging exactly?
As for the iPhone, the latest models are as fresh as ever and the whole point of the article this thread is based on is how spectacularly successful it is. What gives you the impression that it's in any way tiring? Sales? Revenue? Margin? All as healthy as ever. The demise of the iPhone has been predicted for all the 8 years it's been on the market, but the fact is there's no indication that it's anywhere near peaking yet.