I'm sorry what? Settings -> Apple ID & Purchases -> Subscriptions -> Choose subscription -> Cancel Subscription
Or if going into the phone settings to manage your app store subscriptions doesn't make sense to you, there's also App Store -> Account -> Subscriptions -> Choose subscription -> Cancel subscription
It even tells you both when the subscription renews and how long you can keep using the features for even if you unsubscribe. Once you unsubscribe that's it. Since the purchases go through Apple, unsubscribing means the developer can't pull a Comcast and "forget".
I even just now grabbed and app and started a "free 1 month trial" for their service. It shows up in the same subscription list and tells me when it will renew and how much it will charge me. If I tell it to cancel the free trial, it even lets me know that I can continue to access the trial services until the end of the trial period next month.
How is any of that "an obstacle course"? Yes, I agree that it would be nice if trials defaulted to not auto-renewing or you were given a choice when starting a subscription. But managing what you're subscribed to is about as simple as it gets.
Maybe the author is talking about an app that you subscribe to outside of the app store (e.g. Netflix or Spotify style). Certainly I can appreciate that you can lose track of your subscription there, but I fail to see how apple has any responsibility for "not protecting" you if you don't actually go through their processes for being protected.