I have been working in ADF for more than 10 years now, and lots has changed during this time frame. As per my experience:
1. ADF is still holding good in the web based complex business application targeting UI on Laptops desktops, for Mobile MAF was good but considering the Licensing and now the Oracle strategy, MAF doesn't look good.
2. Mobile application are smaller and targeted for specific tasks or flows, so its better to start with approach where you build the business logic in the rest services first for the targeted process, you can do this by any tech:
- APEX/ORDS if your most of the business logic is in ORACLE Database.
- ADF BC: if you want to reuse the logic from ADF application.
- Spring Boot/Node JS (Open source)
Also If you have access to oracle cloud then you could easily setup your environment and to see which of the above suits your requirement better.
3. Mobile application building has two approach one is Native and other is hybrid. For me Hybrid approach suits well, as it can be targeted to different platforms and screens sizes and I feel this approach is more refined now.
for UI you can use again Tech like Oracle JET/Angular/ React JS (this is new for me as well, but good learning)
I am following this approach for enhancing our applications as well and also playing with Bots and other interesting stuff on oracle cloud.
I hope if this helps and @GURUS please Correct me if I am missing any point.