I'm more inclined to think that "fair usage" distinction lies between 50 - 100GB. 200 GB would means one would be using near 7 GB per day. I don't know of any activities that you could do normally on a phone that would have you hitting 7 GB per day, everyday, for a month. FLOW's Home LTE service gives about 100 GB per month. For that reason, I think the network would want to keep service quality high.
[They also announced another mobile network upgrade through to Monday AM, btw.]
As to Digicel, they've got some serious catching up to do. FLOW'd hit their population target (95%) for LTE coverage well before anyone else had anticipated. Now, they're working on the network core again; 2020 is likely to be another solid year if these upgrades deliver. All you really need is a solid, simplified radio network and some serious backhaul.
Also, to your point on HFC -- it is going to continue to serve us here for at least the next 3 years. HFC is still cranking out award-winning speeds around the world. The malaise our networks suffer from is underinvestment. DOCSIS 3.1 & 4.0 can push up to symmetric Gigabit speeds. VTR Chile & UPC Switzerland, sister companies of FLOW, use the same TG2492LG modems as do we and receive speeds up to a gigabit through HFC. Do watch out for the TG3492LG-FLO; it has already been certified for use in Jamaica by the SMA and wide-scale deployment would mean FLOW's either going 32x8 channel bonding on DOCSIS 3.0 or going to DOCSIS 3.1. Islandwide fibre is the outlook (according to FLOW) for the next three years.