Hi, Not exactly.
Proxies are useful because they limit the time the users private key has to be unencrypted.
PKI really relies on the ready availability of the users public key. Hence we create proxy to limit the exposure to our public key. I'm not an expert in this area, but my impression was that the proxies were short-lived because they used a less secure, but faster, method or key length for encrypting communications. The drawback of the RSA-like algorithms is that they are relatively slow. From this, it would seem that a minimum key length would be a necessary and sufficient requirement for a directory of public keys.