Rabbi, what about what we say after the blessing over Torah study, “These are the things that have no fixed measure,” etc.? Isn’t that somewhat ethical instruction?

I don’t think so. Most of them are matters that have a minimal positive threshold, and anything beyond that is optional fulfillment. Both the obligatory minimum and the optional fulfillment are part of Jewish law (these are commandments). By contrast, ethics is usually not in the realm of Jewish law at all.
I have always held that, contrary to what several later authorities and medieval authorities wrote regarding positive commandments dependent on time, namely that these are optional commandments for women, in my opinion they are not optional commandments at all, but simply not commandments. It is the performance of a positive act that is not Jewish law. An optional commandment (according to the one who holds that there is even such a thing; as is well known, Rabbi Moshe Feinstein and Rabbi Avraham Shapira disagreed about this regarding settling the Land of Israel) is part of Jewish law (there is no optional commandment without a command in the Torah). It is hard to define what practical difference this makes, and I initially thought the practical difference was regarding overriding a prohibition (an optional positive commandment also overrides a prohibition, whereas ethics does not). However, the Raavad at the beginning of Sifra writes about time-bound positive commandments for women (women may perform laying hands voluntarily) that it does override a prohibition, and this requires further analysis.

Obviously one does not recite the blessing over Torah study on ethics. The strictest opinion in the Talmud (Berakhot 11b) says that one recites a blessing over Talmudic study because the Jewish laws are clarified there. The dissenting view apparently holds that one does not recite a blessing over Talmudic study because it consists of dialectics and not decided Jewish law. There are also opinions that one recites a blessing only over Scripture or halakhic midrash. But no opinion would require a blessing over ethical works, and anyone willing to listen and not just follow what “common practice” does will see that this is completely proven from the Talmud.

So if one studies the verse in Proverbs, “Do not rejoice when your enemy falls,” one recites a blessing, but if one studies the mishnah in Avot, “Shmuel the Small says: Do not rejoice when your enemy falls,” then one does not recite a blessing?

That’s demagoguery. You recite the blessing because of the verse.