That is a reasonable observation to make. We can always flip the narrative and look at the 'overall average' lap time but sorted in order of the team's FTD. If you stand far away from the graph and squint your eyes, sure you could argue the trend that is going upwards in that faster cars are faster on average, but there is ton of variance in the data that, in counter argument, far exceeds the magnitude of the trend. It makes sense that fast cars can go fast, but fast cars can also go really slow. Of course preferable to have the faster car, but I agree that the pit stops and driver skill do have a big impact on overall placing.
This is where the rising lap time plots are fun to look at. Where the lines cross over is when one team begins to outperform another, though its tough to really see how the pit stop battles play out - it's better at showing the differences in race pace. Just imagine a race where your laps had to be in order of ascending lap time... the race would end with teams waiting to get out of the pits. Kind of odd to think about.
The vertical axes can hide the subtleties in the plot, so good on you for catching that. Here is the plot as a percentage increase over the event FTD - simply a rescaled version of the plot above.
That car you see on the far right side is about 21% slower than the FTD set by Not Banned Yet.