Responsive design in Storyline 360

That's a really narrow perspective, seeing this from the inside out (instead of from the customers POV). Sounds a lot like the older generation telling young people it's useless to watch movies on mobile devices. If you have clients where a lot of the people in the target group do not have a computer you simply have to adapt. The decision to do all development in Rise from now on was not made by an end user but the head of competence development.

I would not be surprised if SL lost a lot of market shares the next few years due to the fact you cannot produce courses adapted for mobile devices.