Is mobile data more reliable than my resort's Wi-Fi?

Yes, for mobility and price. Most luxury resorts (in Soufrière or Rodney Bay) charge high fees for Wi-Fi, and it's often slow or only works in the lobby. A personal eSIM gives you a private, fast 4G connection that works in your room, by the pool, and, most importantly, when you leave the resort to explore the island's beaches and waterfalls.