I don't know what are you asking for.

Why is it more secure using Gmail +  GPG or Delta.Chat ?
Your keys your data.

Protonmail scans your emails and possesses your private keys.

Why I don't use Gmail?

I don't like it. 

 Thank you for the explanation. 

  https://i.nostrimg.com/f04a6c94e7ab238a2e30aede3f5ab8bc348e4af2721685e6d2072e72b14e1979/file.jpeg