Half a lesson in oath

Does the following move seem to you to be proof that one does not commit to half a shiur in an oath, contrary to the opinion of Rabbi Akiva? First, from the principle that no oath applies to an oath, we learn that if I swear not to eat pork, then the oath does not apply because I have already stood and sworn from Sinai. Likewise, when I swear not to eat pork, I do not explicitly state ‘except for half a shiur’, and if you say that when a person swears he intends to forbid himself from eating pork as well, then certainly when I swear to eat pork it is a different mitzvah, since half a shiur is not forbidden in the same way that a full shiur is forbidden. If so, then it is obligatory that even when I swear on something that is permitted, I deduct half a shiur from the oath by implication, since we have not found a difference of opinion in a person between an oath on a prohibition or on a permit. This is contrary to the opinion, because on the face of it it sounds like the shiur are a halakhah from Moses from Sinai, therefore it is not reasonable to include them in a person’s opinion. And perhaps you will say that all of this is true since they were not given, but since they were given, the simple assumption is that we were educated on them and that is how we see things. And perhaps there is also a hidden assumption here that it is appropriate for a person who is educated according to Torah law to practice swearing and swearing on the other side in the same way that it would be forbidden if there were a prohibition.