The thing about standard libraries, like Arduboy2, is that if you remove a documented API function that has been used in a sketch, then that sketch will break when compiled with the new library release. It's better to leave the old function there even if the new function is improved in a way that leaves no reason to use the old one for new development.
In the specific case of drawCompressed(), one could argue that there are currently very few sketches using Arduboy2 so far, and the chances that any are using drawCompressed() is very likely zero, so nothing would break by removing it.
However, it's unknown if there are some games in development and are near completion in which the author has chosen to use Arduboy2 with drawCompressed(). If the function were removed it may cause the release of a game to be delayed because the developer would have to spend time recompressing the bitmaps and switching to the new function.
It's also possible that someone may wish to modify or extend a Team A.R.G. game but wants to take advantage of something that Arglib can't do but Arduboy2 can, such as playing multi-tone effects using the ArduboyTones library instead of the simple single tone function in Arglib. Since I've made Arduboy2 highly Arglib compatible, replacing Arglib with Arduboy2 is generally quite easy (as I found with the 4 that I quickly converted). If drawCompressed() were removed, it may make doing this kind if thing a more difficult.
If it turns out that drawCompressed() has no benefit whatsoever over the new function then I would note that fact in the documentation, recommending the new function be used for all new development.