There is no requirement anywhere that a replacement tire must have the same capacity or greater than the OE tires. The only requirement is that the tires capacity must meet or exceed the gross axle (GAWR) rating.
LT tires are great choices provided they have the capacity of the (GAWR). ST tires are speed limited to 65 mph as that is why they carry a higher load rating. The only problem is that if you run them at or near their capacity at that speed they will degrade and fail quite soon. LT tires are made to run 24-7 at their capacity at a much higher speed.
Your choice, your money and your trailer.
Keith