I've only been 3D modelling for a few days now, so this may just be a newbie mistake:
However, because this model is for use in a game I am trying to stay away from proximity loops for performance reasons. Instead, I have used edge creases to maintain the structure of the model. It has led to certain vertices not being affected by the subsurf modifier, causing undesirable lighting at high subsurf levels.
Manually moving each point in a bit seems kind of sloppy but I'm not too sure what the best way to go about this is.
If any more information is needed I'll give what I can, thanks in advance :)
The issue is in your topology. I suggest you do something like this :
The idea is that you have to place the basis of topology which the subdivision modifier will follow :
If you do that correctly, you will have the right result.
Also, be aware that using mean crease really should remain as a temporary solution. It's handy for prototyping mostly; because it's fast and doesn't require more work, but it doesn't provide any precise control on the obtained shape and geometry.
I've seen some people using it to create quickly and roughly a basic shape. Once they are happy with the shape and volumes, they add a new object on top of it, add some shrinkwrap modifiers, snapping tools, and they to the final model and focus on topology and shape refining.