Key lengths in asymmetric and symmetric encryption differ at the same security
level.  Thus 2048-4096 bits in asymmetric is roughly equivalent to 128-256 bits
in symmetric. See
https://en.wikipedia.org/wiki/Key_size#Key_size_and_encryption_system.

When it comes to passwords, it's the entropy that matters.  A high key length is
useless if the password entropy is too short.  Ideally, the password entropy
should be about the same as the key length.  See
https://en.wikipedia.org/wiki/Password_strength#Entropy_as_a_measure_of_password_strength.

Conclusion: symmetric encryption is fine for online storage too, provided the
password has 128-bit or more entropy.  A master password is often necessary.
The advantage of asymmetric cryptography is that master password are de facto in
place.

This particularly useful for local testing.