AS/400 vs ?
The AS/400 was to many customers the Vista of IBM. Slow, overpriced, buggy, with difficult and time consuming management processes.
Although you are correct in saying that the AS/400 was a continuation of S/38 technology, most applications for the AS/400 were originally written for the System /36 which the AS/400 was meant to replace. It didn't. In fact the System /36 continued to be sold as an AS/400 model for the next ten years. Some applications were re-written for RPG/400 but most large packages still had huge amounts of S/36 code.
The AS/400 was the death knell for IBM in the small to medium business. It should have been a lesson for all OS suppliers. The new version of the software should be faster, with more features and better value for money. IBM went away from that with its s/36 customers.