Alain, Try not to confuse a piston engine at MCT with a turbine at MCT.
Running a turbine at MCT does not decrease reliability or increase the likely hood of an engine failure. It just increases the cost of overhaul and reduces the time on wing due usually due to reduced EGT margin caused by the higher temp and RPM.
Generally for a given engine, more thrust = reduced life = more cost which is why operators try to keep thrust use to as low as possible.
Engines such as the CF6 (LM2500 for example) run for hundreds of thousands of hours at maximum power in electrical power generations.