What are you using for playback that needs a codec pack? VLC and MPC-BE both use their own built in filters unless overridden.
EDIT: Besides when ripping BDs, I haven't had to use video / audio DirectShow filters in like 5+ years.
I used to use it quite extensively when watching older anime rips. You're right thought that DirectShow isn't really necessary for anything anymore which is why I didn't mention it originally.