The whole "Midsize" and "Full-size" terms are for marketing purposes, much like "Military Grade," which makes the material or object sound tough and durable, as opposed to Military Spec (mil spec) which are a set of standards commodities must meet or exceed. The EPA classifies cars based on interior volume, and trucks based on Gross Vehicle Weight Rating (GVWR). Pickup Trucks are either Small: GVWR <6,000 lb (2,700 kg), or Large: 6,000–8,500 lb (2,700–3,850 kg). There is no "Midsize" truck class officially. So, the Maverick is a Small truck at 5,231 lb (2373 kg), and the Ranger is a Standard truck with a GVWR ranging from 6,050 lb (2,733 kg) to 6790 lb (3,080 kg) depending on powertrain; right in there with its Super Duty brethren.
When or if a CE-1 or -2 BEV pickup comes out it will probably exceed the Small category, but will be probably be marketed as a Built Ford Tough Midsize Truck.