What, you ask, is the difference between the “inclusivist” stance of the contemporary Roman Catholic Church and the position of the Christian perennialist? Are they basically saying the same thing?
By no means.
The Catholic inclusivist allows for the possible salvation of non-Christians, but only on explicitly Christian terms. A Buddhist, for example, may well be on his way toward salvation, but if so it’s only through the mediation, unbeknownst to him, of the historically crucified Christ.
For the Christian perennialist, however, if and when a Buddhist is “saved”—I put this word in quotation marks as a reminder that “salvation” is a distinctively Christian category and that Buddhism describes human fulfillment in other ways—it’s by a “Christic” means unbeknownst to Christians.