Although if a dishwasher does the same job, then it really does seem that you could use a dishwasher too.

It is fairly clear that utensils in the past had a very different material density. The medieval authorities describe that during the kashering process, the water becomes dirty from the fat that is expelled, if I remember correctly. That does not happen today.
So nowadays each utensil needs to be checked on its own merits.

And what is your view regarding the scientific question? Does kashering nowadays, for example in boiling water, really make a difference regarding the amount of forbidden substance absorbed in the utensil? For example, if we assume utensil X had some forbidden substance absorbed in it, do you think that after kashering the amount of absorbed substance, Y, is at least less than X/2?

Tzach,
in my humble opinion, it is clear that the issue is not the density of the material but the existence of soap.
Clean utensils with sand and you will see that the water gets plenty dirty after boiling.

Hello Rabbi, who is Pixler?

I looked again a bit at the materials by Pixler and Fink, and I did not see any reference there to the question of the effectiveness of kashering by boiling (and in general I did not see any discussion of this question online). The discussion I found was mainly about whether there is absorption or release in utensils, but not about the question that if we assume there is absorption/release, what the efficiency of kashering utensils is in preventing it. If you had to make an educated guess about this question, what would your hypothesis be? And if, for the sake of argument, the answer to this question were negative (that kashering is not effective), would that permit using utensils even without kashering? Or perhaps would it completely prohibit using utensils in which a forbidden substance had been absorbed even after they were kashered?

Rabbi Professor Dror Pixler from Bar-Ilan.

I do not have an intelligent guess. The whole subject of absorption is not scientifically familiar to me.
It is hard for me to believe that kashering makes no difference while cooking does cause absorption.
In order to determine a halakhic position on these questions, comprehensive research is needed: what happens in absorption, in kashering, what is really absorbed in utensils, and what is released. It is not serious to answer this based on mere intuition, especially since I do not even have an intuition.

And if we assume for the sake of discussion that there were an experiment showing that kashering utensils is almost useless for removing the absorbed substance, would that permit using utensils even without kashering? Or perhaps would it completely prohibit using utensils in which a forbidden substance had been absorbed even after they were kashered?

As I wrote, it is impossible to answer this without understanding whether and how much is absorbed, whether and how much is released in cooking, and so on.

Let us assume for the sake of discussion that the amount of absorption and release is like what was measured in the experiment by Pixler and Fink.

I do not know what they measured.

By the way, it is Frank, not Fink.

In the summary of their experiment they write that the rate of absorption and release is "very small" and does not come close to the ratio of one in sixty.

If so, then apparently there is no problem. Of course, for a result to gain scientific validity, others need to replicate it and there needs to be discussion of its assumptions and methodology.