The whole point is that you don't just use it to upload a key. You link various verified identifies of yours across the web to your Keybase account so people know the PGP key there is the one of the verified person. It's a way to tie all your verified identifies together.

If someone would manage to compromise a bunch of identities of someone on the internet, and then create a Keybase account with them and then upload a compromised PGP key that would be a problem if you don't verify the key. But that's a bit of a stretch.

My real wish is that keybase supported ssh keys and would provide them as an agent.

I do agree on the ssh key feature being nice, and, here's a link: https://keybase.io/blog/keybase-ssh-ca You could also just use the keybase file system to keep ssh keys around.