This is the 3rd time I am entering this response. I’m putting it here because when I put it in the Discussion box, it keeps disappearing.
There are many products available to assist you in building dashboards and to easily create web interfaces to your AS400 data.
I would look at doing some of that to help change the perception that the AS400 is not a modern machine.
The last place I was at had many COBOL programs which we slowly phased out by rewriting them with RPG programs.
I would suggest you hire new staff that have the skills to do these tasks for you. They can exchange knowledge with your current staff so that you have a good foundation for moving forward.