I'm a big fan of his but that's a fair assessment to make and I can see where you're coming from especially seeing as his goal scoring capabilities has basically stayed at the same level for the past 3 or so seasons in a row without an improvement. He looked a much more rounded player to me in his breakthrough season than he has shown here though that probably has more to do with the fact that his position and what is expected from him has changed from what it was at liverpool. He was a no 10 with two top strikers at the time ahead of him at liverpool who stretched play and defenders so allowed him the freedom to thrive in that role in his breakthrough year while last season under pep, he was mainly tasked with hugging the touchline and being a creative output from wide for aguero, sane and any of de bruyne/silva that arrive late in the box and for the majority of the season he delivered on that. I believe his decision making has improved from when he was at liverpool but yes there hasn't been that much of an overall improvement in his game from that breakthough season.
The thing with young players though especially the wonder kids(which sterling was at that time) is not many improve their game much from their breakthrough season till they reach around 24-25. There are slight improvement here and there in their tactical understanding and decision making through experience but not many are able to improve much in their overall game especially on the technical side. Sterling is currently at a point where the only major improvement he needs in his game is his technical side in how to strike a ball well especially when shooting. His mental side of the game is already at a high level in terms of the tactical intelligence he has and positional play. Its his technical side that's holding him back from moving into the next level. At 22 he is still young(just a year older than sane) and is no way near reaching the ages where major improvements or consistent application of his attributes are to be expected. Look at how inconsistent a player of De bruyne's quality was last season to see that consistency at the highest level is rare even for world class players.
All things considered even at his current level, its pretty clear he's become a very important part of the side in the past couple of season, you only need to look at his champions league performances to see that where imo he's been the best performer over the last two seasons in that competition. Whenever he's not in the side its felt as there is not a player in the whole squad who's as intelligent and dynamic in their movement as he is which not only gets him in many dangerous goal-scoring/chance creating situations but also stretches the opposition defences and creates space for the other attackers and midfielders to perform particularly against teams that looks to defend.