I’m having trouble understanding beliah of vessels in contemporary times. Do we not consider modern cookware’s advantage, as opposed to Talmudic era conditions, in preventing taam infusion?
Here is my question: Shouldn’t stainless steel have the same status as glass (Sephardically speaking)? Stainless steel "does not corrode, rust, or stain with water," is completely non-porous and thus, practically speaking, does not absorb. There are probably other examples, but this jumped out at me as the most obvious and profuse.
Should we not consider this scientific wonder in clarifying modern halakhic dilemmas?
Your question has been titled "Modern Vessel Absorption" - but really your question has been around for a long time. The same question was posed in relation to glass, which only became widespread in the times of the Maccabees during the second Temple period. As you might be aware, there are three opinions about the halachic absorption quality of glass, and the need to kosher it. One opinion says that glass is non-absorbing, and as such it does not need to be koshered at all. Another says it is like metals, and needs to be koshered. The third opinion holds that because the basic material used to make glass is sand, it has the law of a vessel made from sand and clay, which is that it cannot be koshered at all. From this we can see that there is a fundamental argument about how to classify vessels - whether by their actual ability to absorb taste, or whether by their original material matter, regardless of the end product's apparent porousness.
We could perhaps relate the same argument to newer metals, and in fact Rav Moshe Feinstein zt"l raises this issue in relation to aluminium. He writes (O.H. volume 3, 58) that there is a doubt about how to kosher aluminium because it is composed in some part of substances not listed in the Torah as metals, and perhaps therefore it would have the law of non-metal vessels that cannot be koshered. On the other hand, perhaps as it appears to be non-absorbent it does not need to be koshered at all. His conclusion is to kosher them as we do all metal pots.
I have not seen any direct sources relating to stainless steel, but the custom is certainly to kosher them like all other metal vessels. The reason for this is probably twofold. Firstly, perhaps the halacha is that we define the vessel by the original substances used in its make-up, and as such the steel in the pot would cause it to be defined as a metal pot, despite the fact that it now is non-absorbent. In fact this is (as you hinted in your question) the way Ashkenazim treat glass. Secondly, it could be that the halacha does not distinguish between the actual absorption of each type of pot, but rather places vessels into general categories (this is called in halachic terminology "lo plug"). If so, then because the Torah stated that metal pots need to koshered from their absorbed tastes, all metal vessels have this status despite their individual qualities.
So, in conclusion, your question is a good one, and certainly halacha understands and considers the scientific status of different materials. This though is not the only consideration, and is only a part of the total halachic reasoning. The practical halachic conclusion of the codifiers is to kosher all metal vessels, no matter what metal they are made of, in the same fashion we have always koshered basic metal pots.