There's not much to learn from this question because on the face of it, increasing any of these three has the potential to increase the plant growth rate. But this is too simplistic. Is the point to maximize growth rate or is to maximize plant health? Increasing the light without regard to the other two components will generate higher growth rates but also has the potential to create a deficiency in the nutrient/CO2 uptake. So the actual numerical value of "X" is important and at the same time few people actually know the numerical values, or at what numerical values the deficiencies are developed in the other "X's".
Therefore, there is no point chasing "X" other than to know that there are some PAR values that make life difficult, medium, or easy in obtaining decent growth rates while fostering decent plant health. They are all interactive with each other and they each have certain practical characteristics. As Edvert mentions, CO2 is extremely difficult to optimize but it's very easy to turn on a light switch and very easy to dump nutrients into the water column.
So, since light drives the requirement for the other two components you have a situation where it's easy to increase the light but extremely difficult to increase the CO2. The obvious solution is to limit the light input to the tank so that it will be either easier to either improve the effect of the CO2 addition, or will require less CO2.
Adding light is like increasing the speed while driving your car. The more light you add the smaller the mistake is needed to careen out of control.
There is no relationship between the rate of plant growth and the level of plant health. This is a key point that most people consistently misunderstand. Plants can have a high growth rate and yet be miserably unhealthy. Conversely, growth can be agonizingly slow, yet the plants can be in picture perfect health.
When a tank is first set up it always looks bland and uninspiring due to the shortage of plant mass, so everyone immediately has the objective in increasing the growth rate as quickly as possible and the decisions made regarding tank management are always within the context of this objective - and that's where the trouble starts, because the growth rate priority is almost always to the exclusion of other, more important factors that govern plant health.
The best path is to use 0.1X light + 50X nutrients + 100X CO2. This will minimize most problems.
Cheers,