The closeness to Mesora has always been primary. Halacha LeMoshe Misinai is immutable. Torah Shebaal Peh as written is a record of Mesora including contradictions and attempts to disambiguate and show through the Midos SheHatorah Nidreshes BoHem, including Sevara (which isn’t listed but is clearly a Midda as testified by the Gemora in many cases). As time advanced through Tanaim, Amoraim, Geonim, Rishonim we move to latter generations known as Acharonim. To be sure, there are some Acharonim, who on occasion would argue with Rishonim. Two well known examples are the Vilna Gaon and the Rogachover. They were guided by what they felt was Emes L’Amito.
When it comes to Acharonim, there are those, depending on which group you align yourself with, who are considered “the last word” and there are others, such as the Chazon Ish in respect of electricity where everyone seems to be Chosesh to some extent to his opinion. That being said, others will say he was an Acharon in B’Nei Brak and if he was your Rav and/or you lived there you need to follow his Psokim.
The Brisker Shitta, is different. Whilst they are beholden to Beis HoRav (Volozhin/Soloveitchik) they were never afraid to disagree with each other. Of course, there is a group that follows every word of Reb Meshulam Soloveitchik, son of the Griz (Uncle of the Rav) in the same way that Chassidim follow their Rebbe. He’s just not called a Rebbe, and he doesn’t fir tish etc.
We saw that as a Posek became more recognised, people came for Brachos. Some were averse, and others would give a general Brocha to be Yotze. I sensed this from Videos of R” Shlomo Zalman.
The Rishonim (and here there is some difference amongst Ashkenazim) and certainly Sephardim, are untouchable. If you want to innovate=bring something consonant with Menorah you need to bring a Rishon.
I remember well, some 40 years ago when my zeyda bought a copy of the Meiri. At the time it was very controversial. Beautifully put together, it was ignored somewhat for years. Now, it seems nobody has a problem quoting a Meiri. The Meiri was a Bar Mitzvah present for my cousin Ya’akov Balbin and while it sat in my house for many years after he went on Aliya, I sent it to him at his request.
There have been plenty examples of Ziyuf. There was the fake Yerushalmi on Kodshim, and more.
The common denominator was that to qualify for Psak, especially the style of Psak (especially Hungarian) where one joins different Kulos, you had to have a Rishon (or early Acharon who quoted a Rishon given that some had access to Rishonim we don’t have, or a Girsa we don’t have.
There are stories where the Rav’s Talmidim, would say but Rebbe it’s an open Maharsho that contradicts your Pshat. When he was younger, he angrily banged the Gemora and said, “and I’m not an Acharon”? This was not haughty. This was what he felt. He felt his Pshat was more correct than the Maharsho and was ready to debate it with anyone.
Many Acharonim either didn’t own, or look at other Acharonim. That’s not to lessen their importance. But, it’s a derech.
Where Chassidim/Mekubalim are different, I feel is that they would consider that when there is no clear way forward or where there are different views, Kabbola, whether from the Zohar or Ari on occasion trumps and guides the Psak. A pure non Chossid/Mekubal would note such opinions but would be less likely to PASKEN based on them.
Do people agree with me or have I over simplified. Drush is another class. One has license to extrapolate and certainly doesn’t need a Rishon to find a nice Pshat.