You get the interface and speed you prefer. Cons: You miss out on security patches and new features. Google often updates the API (the backend connection). Eventually, version 5.11 may stop connecting to YouTube's servers entirely, forcing you to update.
Users seeking a specific, older version of YouTube Studio generally fall into three categories:
There are third-party apps like "YT Studio Lite" or "TubeBuddy" that offer lightweight interfaces. However, give them limited permissions and never share your Google password.