If I were choosing disc brakes for serious MTB use I would also have gone for hydraulics. However, for a mostly road ridden "Gravel Bike", the simplicity and ease of maintenance of mechanical discs was too attractive to pass up and I've been very pleased with my Spyres. I ride plenty of sizeable hills and they have been completely satisfactory.

As to brakes failing from cables fraying, any cable operated brake is susceptible to that and regular cable inspection and replacement is only common sense.