Contemporary fantasy can be very engaging when it's well done (for example, I like the Bartimäus books) but also has a few stumbling blocks that FF15 sadly stumbled upon. As an example, FF15 features super modern flying cars and smartphones but you still have to travel hours from person A to person B to get the information from B that the bean carrying truck has been attacked thus B can't carry the beans to A in time. After aquiring this information you travel the same amount of hours back to A to tell him just this information that everyone with a smartphone could've delivered in a minute. Yes, you could raise objections here, but I guess my point is clear. You have radios everywhere that cover the latest news about Noctis having evaded his death, still you see not a single wanted poster or bounty hunter anywhere. Small things like this just ruin a piece of the immersion and believability because things need to be explained that would otherwise be glossed over by "it's magic" or "we only have horses, if even, so no shortcuts".
I don't know what mechanics fantasy is, either. Do you mean Mecha stuff like it's featured in Gundam, Code Geass or Eureka Seven?