The You Tube video that everyone is watching has brought this question to the forefront.
R' Hoffman wrote a response The Avos and the Mitzvos, where he claimed that there are 3 opinions, minimalist, middle and maximalist, where he recommended teaching the maximalist position. He also claimed that the video mocked both the maximalist position as well as R' Elyashiv.
IMHO, the video mocked neither. The video mocked those who take the maximalist position to ridiculous extremes.
The fact is that even the maximalist position is not so maximalist.
The same Radvaz who R' Hoffman claims is a maximalist discusses a similar question in a teshuva. He discusses what does it mean that the Torah existed before creation. He quotes Chazal who describe the discussion between the Moshe Rabenu and the Malachim when Moshe went to get the Torah. The Malachim asked how can Hashem give the torah to man? Moshe answered it says in the Torah לא תנאף does that apply to Malachim? It says לא תחמד does that apply to Malachim? etc.
The Radvaz asks what was the Malachim's question and what was Moshe's answer? They didn't know that it says לא תחמד in the Torah? He answers that the Malachim understood Torah on a different plane. They saw Torah as a description of אלוקות, they didn't know about the mitzvos that relate to man. Moshe explained to them that the Torah has another level of meaning where it requires certain mitzvos that only apply to man. He explains that before matan torah the letters of the Torah existed but not in the same order/words that we have. In fact, the Ramban in his introduction to his commentary on Chumash makes the same point. The Gra also is quoted as saying this. The Gemara in Bava Basra has a discussion about who wrote the last 8 pesukim in the torah. One opinion is that Moshe wrote it בדמע. The regular pshat is tears. The Gra however is quoted as saying that דמע is from לשון דמאי, something that is mixed up. He says that Moshe wrote the letters but not the way we read them today. In short, they all say that before Matan Torah the Torah existed in a different state then what we received at Har Sinai.
It is clear that the same thing applies to those who hold from the maximalist position. The Avos were mekayem the mitzvos based on their understanding of how to serve hashem. How to serve Hashem was different then it is now. That is why Yaakov could build a מצבה, Yehuda could perform Yibum with his daughter in-law, Amram could marry his aunt, etc. They fulfilled those mitzvos that made sense to fulfill.
I would like to make another point. Just because Rashi quotes a midrash doesn't mean he holds from it. Rashi quotes midrashim to explain the text, if a midrash explains the text well Rashi will quote it. There are places where Rashi quotes Midrashim that contradict each other.
A few quick examples. In ויצא Rashi quotes Chazal that Dina was conceived as a boy and Leah davened and a נס happened and she turned into a girl. Yet Rashi quotes in Vayigash on the pasuk ואת דינה בתו that the man is responsible for conceiving a daughter. The Maharsha in Nida points out the contradiction and answers that the Gemara in Nidda had a different pshat in ויצא (see my post The interesting story of Dina and Yosef for a full explanation). Yet, Rashi quoted both. Similarly Rashi says that Avos kept all of the Mitzvos yet Rashi says in Vayigash that Shimon married Dina which is clearly prohibited. The Maharal there answers that he saw ברוח הקדש that it was permitted. We see that things are not as simple as they appear.
My point is that it is impossible to take a completely literalist/maximalist approach to the Gemara in Yoma 28b. There are too many examples of things that the Avos did contrary to halacha.
R' Hoffman claims that the majority opinion is the maximalist one. I am not sure where he got that from. In any case, I happened to see that the Meshech Chochma (33:18) seems to take a minimalist view. He explains the Gemara in Yoma 28b that Avraham kept Eruv Tavshilin as a מליצה (an expression) to mean that Avraham was involved in הכנסת אורחים. So we find a 20th century mainstream Acharon taking the minimalist view.
Here is the video that is causing the storm.