Part of the reason why there is so much confusion about RCIA is that in the majority of parishes in the U.S., the RCIA programs are not being properly followed (note the plural—there are different forms of RCIA, not just one).
There is RCIA for the unbaptized. That form culminates in the reception of Baptism, Confirmation, and First Communion at the Easter Vigil Mass.
Another form of RCIA is for those already baptized outside the Catholic Church. This is a different form, and is not directly related to the Easter Vigil Mass.
The problem comes in when the 2 forms are combined into a single group of people. Now, there are practical reasons for doing this, no doubt. There are positive values to doing it this way (often people in both groups share the same questions and need the same catechesis.)
With that in mind, when we get back to the original topic, it’s only natural that questions and comments like:
“why must non-Catholic Christians wait until the Easter Vigil?”
or
“non-Catholics don’t always have to wait until the Easter Vigil, therefore if we can make an exception sometimes, we can broaden those exceptions”
These miss the point.
The requirements for an adult who is already baptized, but non-Catholic to receive Confession, Confirmation, and Communion are all the same requirements (taking into account, naturally, that Confession must come first). That means that an adult who is properly prepared and eligible to receive Communion is likewise eligible to be Confirmed.
The only issue here is whether or not the parish pastor has been given faculties by the bishop to confirm adult converts. The person is eligible, but the pastor might or might-not have faculties.
While I recognize that there can be some positive values in combining two forms of RCIA into a single group (the non-baptized and the baptized), this practice opens up a wealth of other problems, and a great deal of confusion and misunderstandings. Precisely the kind of misunderstandings that arise when we discuss the topic of this thread.