The good thing about "telemetry through achievements" is that players can see it too. It gives a good baseline about the other non-obvious achievements.
For instance, an achievement that has about the same unlock rate as the "complete stage 1" achievement is probably something you stumble upon randomly in the very beginning of the game, if you don't have it, you probably missed something. If an achievement has a significantly lower unlock rate than "complete the game", it is probably end game content and may require dedication.
Achievement can have more than one purpose. They can be used as progression markers (the "tutorial complete" kind). As hints about some secondary content. As a reward for curiosity or particularly difficult tasks. As an indication that you have finished something and there is no more of it. To taunt the player. As objectives that don't fit in the story. To acknowledge that a particular action is significant. Etc...
For example "Use the Batarang for the first time" tells you that you will use it again. It hints that from now on, the Batarang will be an important part of gameplay, more important than the other items you didn't get an achievement for. On the achievement list, it is a progression marker. If you see it on an achievement list, it tells that the players is, say, at least 10% into the game, and puts other achievements in perspective.
The functionality of achievements as transparent telemetry seems entirely accidental, but may be the most valuable aspect of them. Now a developer can look at similar games to the one they're developing and see what filtered players (although it won't tell them why it filtered players, since 'too difficult' and 'boring' look the same in the stats). They can see what endings were popular (which usually translates to some measure of popularity score for characters, factions or whatever. That kind of info is usually traded behind closed doors for extortionate sums.
If the game would only have worthwhile achievements then something like a quest log would be suffice for the non-obvious ones. A quest log and quest item tab can be used to ensure the player knows they'll reuse an item.
What if it's a game without a quest log? Achievements are just a universal framework for this kind of thing. So developers don't have to reinvent the wheel with every game. Sounds like the kind of standardization that is a good thing for everybody involved, except for the gatekeepers who only want hard "achievements".
But one that has to be implemented from scratch by every developer. It's not universal. You can't just redefine shit because you don't like achievements.
Both have to be developed from scratch, and the gamification of meaningless achievements is a relatively new phenomenon in gaming. For example, in WoW they were added in 2008 (WotLK) and in CoD the original MW (CoD4) didn't have it. But they both had quest logs.
For instance, an achievement that has about the same unlock rate as the "complete stage 1" achievement is probably something you stumble upon randomly in the very beginning of the game, if you don't have it, you probably missed something. If an achievement has a significantly lower unlock rate than "complete the game", it is probably end game content and may require dedication.
Achievement can have more than one purpose. They can be used as progression markers (the "tutorial complete" kind). As hints about some secondary content. As a reward for curiosity or particularly difficult tasks. As an indication that you have finished something and there is no more of it. To taunt the player. As objectives that don't fit in the story. To acknowledge that a particular action is significant. Etc...
For example "Use the Batarang for the first time" tells you that you will use it again. It hints that from now on, the Batarang will be an important part of gameplay, more important than the other items you didn't get an achievement for. On the achievement list, it is a progression marker. If you see it on an achievement list, it tells that the players is, say, at least 10% into the game, and puts other achievements in perspective.