Ask which two temperatures were compared
A technician may compare air entering the indoor equipment with air leaving it. That is a different question from comparing an outdoor thermometer with the thermostat inside. Ask where the readings were taken, when they were taken, and what result is expected for your model under those conditions.
A single reading at a distant register should not be treated as a full diagnosis. Request the other findings used to judge the system, including airflow and the equipment's operating measurements. These are professional checks, not instructions to place instruments inside equipment.
Look at the whole cooling problem
Write down the thermostat setting, indoor temperature, time of day, outdoor conditions, and rooms that feel hottest. Note whether the problem happens only during the hottest part of a very hot day or also on ordinary days. Include any recent change in cooling, noise, airflow, or ice.
Ask the technician to distinguish three possibilities: the AC is not delivering its expected cooling, the home needs more cooling than the present system can provide under those conditions, or cooled air is not reaching the rooms well. The correction should follow the finding.
We would not recommend a larger unit simply because the thermostat misses your target. First request the cooling-load calculation and the measured performance of the installed system. Otherwise, a replacement could carry the same comfort problem forward.
Make the recommendation usable
Ask, “What indoor condition was this installation designed to maintain, at what outdoor condition, and what is preventing it today?” If the weather exceeds the design conditions, ask what practical improvements or limits apply. If a fault is found, request its correction and the check that will confirm the result.
Your next step is a documented cooling assessment, not accepting a universal outdoor-temperature rule. That gives you a sound basis for repair, home improvements, or an equipment decision.