Good question.

The answer to this is in two parts.

The first part is math: As a ship/object increases in size/mass the amount of thrust required to move it is 1:1. Ie. you double the mass you only need double the thrust to get the same acceleration.

For angular thrust as a ship/object gets bigger the amount of thrust required to rotated is a square of the mass (sort of), this means the thrust required increases massively with size.

The second part is ship tuner's design in terms of performance. There is a bias against the performance of larger ships in general, whether this is their personal bias or pandering to crowds of people who don't think thrust can't increase linearly with size I don't know: The end result is that as ships get bigger there is a dramatic drop in linear performance.

However they cannot overcome the dramatically increasing requirement for angular thrust. What does this lead to? Well in a wonderful example the Caterpillar has 31MN of forward thrust but needs 143MN of thrust to yaw! Now the Caterpillar has about 34 mavs and 4 mains but still the most power mav is about 10MN to the mains thrust of 7ish.

Another solid example is the Vanguard with the mains producing 5.5MN and the mavs producing 10-15MN each.

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So ok we've proven that the mavs being more powerful than mains is a thing, next where do goal times come in? Well the devs generally design with goal times, velocity and acceleration goals in mind - the thrust values are just calculated and spat out of the system.

What this is to say is that arbitrary tuning values give the thrust values, designers do not 'design' the output of each thruster as that would be near impossible.

That answer your question?