Is a 2" latex topper too thin to get the full effect of firmness versus softness? In other words will a 205# person notice the difference between a firm topper and a soft one or will 205 #s just smash right through that amount of foam?
The effect of a latex topper will depend on it’s ILD, the type of latex, and on the specifics of the layers that are below it are below it. All the layers of a mattress interact with and effect the feel and performance of all the other layers and components above and below it.
How much you notice the effect of any change will also depend on your body type, sleeping positions, sensitivities, the combination of layers you are sleeping on, and where you are in the range inside the “princess and the pea” and “I can sleep on anything” scale of sensitivity. Some people will notice a significant difference with very small changes while others don’t seem to notice any difference between two mattresses that most people would call very different.
There are some general guidelines for toppers in post #8 here but for most people a 2" topper would make a “fair bit” of difference.