'Charting' is not a very useful indicator unless you have current numbers from something lower in the chart. A game which goes on to be a flop can still easily sell more on its first day than some other more successful game on its eg. tenth day.
This is why Steam peak is discussed so often. It's one data point which is always available and often allows for a direct comparison between how many people were playing game x and game y on their first weekend. There are other factors to keep in mind (gamepass/subscription availability, platform skew, did both games launch on steam etc.), but if the context for game x and game y are similar enough, and if you have sales data/announcements for one of those games, you can use it to make an educated guess at the other.
This is why Steam peak is discussed so often. It's one data point which is always available and often allows for a direct comparison between how many people were playing game x and game y on their first weekend. There are other factors to keep in mind (gamepass/subscription availability, platform skew, did both games launch on steam etc.), but if the context for game x and game y are similar enough, and if you have sales data/announcements for one of those games, you can use it to make an educated guess at the other.