It really isn't. Today's unpowered gliders are astoundingly capable compared to anything the Wright brothers lived to see, and that they're not suitable for replacing all of commercial aviation as it exists today should not be taken as a slight against them.
Most of it will need to be replaced by ground-based transport.
The difference is that proton tries to be somewhat interoperable with other services. It uses standard PGP encryption, you can import public keys to it from elsewhere, and you can download your private key from them if you need it.
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Of course I meant that you can easily export the private key from their web client, which is not really a download as such.