Another example of "overpowered" that I can compare to the Megane Trophy is the Cromwell from World of Tanks. In a nutshell, that tank has a really low alpha (the damage each shell does), but to make up for its lack of alpha it has a very quick reload and thus an abnormally high DPM (Damage-per-minute; that is, the amount of damage you would deal per minute assuming that you hit every single round). What makes matters worse for this tank is that the accuracy value of the gun is high, even on the move. It also has a high penetratikn value, meaning that each shot you shoot not only has a high probability of hitting the enemy, but also inflicting damage to them. The tank has crap armor, but amazing mobility to compensate for it
By interpreting "overpowered" literally in World of Tanks, you would think of a tank that has a really high alpha; that is, a very powerful gun. It would also have really good defense. But the Cromwell has the opposites of what I just described as an OP tank, so why is it OP? Because the other statistics it has to compensate for its lack of raw alpha and armor is over-the-top and overkill. Sure, you can trade alpha for DPM, but making it too accurate and too penetrative as well means that you can run around your enemies as they try their damnest to aim at you, while you don't even have to aim at all, or even stop for that matter, because you're almost going to hit and penetrate anyway.
What do tanks have anything to do with the Megane Trophy? From what I understand, your definition of OP is a "Power" car- an RC F maybe, or the old Megane. They have tons of power, and would definitely obliterate the Trophy on the straights. But what the Trophy has to compensate for its lack of straight line speed is its amazing agility, braking, and fuel efficiency. It's okay to sacrifice straight line speed for agility- the 4C does this. It's okay to sacrifice overall pace for fuel efficiency- the GT-R in Gr. 3 does this. But what's not okay is to over-compensate and mash these two things together. What makes the problem worse is its exceptional braking. Most of Gr. 4 cars have more or less the same braking points, but the Trophy can, at times, brake as much as a whole meter board later compared to its peers. It's as if you slapped Gr. 3 grade brakes onto a Gr. 4 machine.
To recap: if your definition of OP is a "power" car, like the RC F, then the Trophy would be out of your radar on the list of cars being OP. However, the other statistics that the Trophy excels to compensate for its lack of power is so over-the-top and overkill that, despite its lack power, it's an overpowered car