Is mobile data more reliable than the Wi-Fi at my all-inclusive resort?

Yes, for mobility and privacy. Most luxury resorts (like Sandals or on the "Platinum Coast") offer Wi-Fi, but it is often slow, shared with all guests, and only works in the lobby. A personal eSIM gives you a private, fast 4G/LTE connection that works everywhere, in your room, by the pool, and, most importantly, when you leave the resort to go to Oistins for the Fish Fry.