How to protect a symmetric key?
As you show in your question, the Microsoft Docs say:


  When a symmetric key is encrypted with a password instead of a certificate (or another key), the TRIPLE DES encryption algorithm is used to encrypt the password. Because of this, keys that are created with a strong encryption algorithm, such as AES, are themselves secured by a weaker algorithm.


This is a simple warning that a key protected by a password is weaker than the same key protected by a certificate.

So, in order to compromise the symmetric key, you need to know the password.  An attacker might obtain the password by cracking the 3-DES encryption; they would then have access to symmetric key, and by extension everything that is protected by that key.

The take-away is, don't use a password to protect a key if the data protected by the key is valuable.  Use a certificate to encrypt the symmetric key.