Although the RDML component of LANSA is relatively easy to learn and use, it does not mean that someone can become an expert without ever having completed a training course.
Additionally, there are many more parts to the development of a complete application than just programming. The Systems Designer(s) must be experienced in database and application design methods that are compatible with 4GL tools, or else have the time available to become familiar with them.
Commencing a 4GL application development without proper education and training is likely to take longer than using existing 3GL techniques.
Training and education involve a lot more than learning how to write programs using the 4GL tool. The construction of application programs is a small part of the complete development cycle.
If you view the introduction of a 4GL tool as simply requiring the retraining of programmers to work in another "language", you will probably not achieve the results you expected.