I think the “sticking as much as possible to standardization” is part of the problem. Your analogy to marriage prep is quite good, IMO. Having gone through marriage prep not too many moons ago, and having gone through all the RCIA process as a sponsor of a good friend, I can comment on both if them. There are lots if hurdles to the marraiage prep, but what works is that it is almost all done one-on-one ( well one on two,ha) . The “test” the couple has to take, and then the follow up review sessions ( with a deacon in my case)are very good. The interviews with the priest are quite good. The only thing that was worthless, IMO, was the thing most like the whole of the RCIA process: the encounter weekend, done in a group setting and taught by very well-intentioned, but obviously amateur volunteers. However, all-in-all, one cannot how through the process and not at the least understand what a catholic marriage is all about.
The RCIA process was almost all ( excepting the liturgical rites) done in group classes and invariably by well-intentioned amateurs. Oh, they had all been trained by the diocese, but were no way qualified to give meaningful instructions of the faith. In every topic, they consistently left out some of the most important points.
Certainly most patishes marry more couples than people brought into the faith via RCIA. So why is individual instruction (by “professionals”)not a key component of the process?