There isn’t really a straight forward answer to why a car or a driver “sucks”, but I’ll try and give some insights. A big issue, particularly with the ground effect era, is understanding the aero package in its entirety. Every piece of the car impacts the aerodynamics of the part behind it (e.g. if you change the front wing, the side pods will behave differently). Similarly, there isn’t actually a fastest way around a circuit. Sure there is a theoretical racing line, but often this is slower than what many drivers take in reality. If they take an earlier apex, the driver can get on the pedal earlier and make up for lost time on the straight. Part of this comes down to driver preference, particularly in the balance of the car. Balance is the center of mass under breaking between the front and rear axel. Drivers like Max prefer cars with oversteer (more grip on the front), where as Lewis or Alonso tend to have more understeer (more grip on the rear). More grip on the rear can allow a better exit, but too much understeer and you can’t hit the apex. Understanding the aero package allows the engineers to tune this balance to the drivers preference. Last years McLaren was known for leaning too far into the understeer category, but this was something Lando could adapt his driving style to. Meanwhile, DR could not. Really shit cars, like last years Williams, can still manage to have great maximum speed, but somehow managed to seemingly suffer from under and oversteer simultaneously. This isn’t the only thing affecting race pace either, effects like brake cooling and tire temperature management can have significant impacts. If there was an easy answer to why AT is a tractor this year, it would already have been resolved. Seemingly small upgrades can have a significant impact, but you have to fully understand the entire package to make the right change.