On a practical level though, the vast majority of Adventists, even those who are more theologically liberal, will see the Sabbath as important.
You have more variety on such questions as the investigative judgment doctrine, etc. A number of clergy and scholars have questioned that doctrine over the years.
It is true that the early Advent movement was not in favor of creeds. And it took some time for the various doctrines to solidify. During the fallout from the disappointment in 1844 those who had participated in the Millerite movement continued to interact in periodicals and gatherings, forming into groups with similar views.
This eventually led to statements about agreed upon matters. They also began to take steps such as ordination of clergy, and property ownership, so that the movement could be more effective in outreach.
Since the dialogue between church officials and Walter Martin regarding whether Adventists were a cult, in the 1950's we see more interaction with Adventist and Evangelicals more broadly. This led to a new publication of doctrinal statements, addressing some critiques by evengelicals.
The introduction of the (at the time 27) fundamental beliefs in the 80s was a continuation of the trend of statements of agreed upon doctrines. But they do spell out quite a bit, so they were more expansive than some earlier statements.
They played an important role in the Desmond Ford discussions, where a prominent professor and teacher of pastors expressed a different view on the investigative judgment doctrine. He was given a hearing, but the documents coming out of the meetings state that they were judging his teaching based on the recently affirmed fundamental belief statements. This resulted in the loss of his ministerial credentials, though not his church membership (he renounced that many years later, as part of an effort to start his own ministry).
The fallout from that was considerable, especially in areas such as Australia and New Zealand, where a sizable group of clergy left, some over theological views, and some simply over the perception of the handling.
In more recent decades, in my opinion, there has also been more willingness on the part of leadership to have a big tent view, not immediately disfellowshipping people if they hold some views not in line with the fundamental beliefs, unless they are particularly vocal about it. And some conferences are more liberal than others, ordaining women clergy locally, though the world church has not approved this, etc.
Even at Christian Forums we see this reflected in the Adventist section, which at one time was one forum. However, as tensions rose between those who held to the fundamental beliefs, and the more progressive members who questioned one or more teaching, the forum was divided into
Traditional Adventists and
Progressive/Evangelical Adventists. They had difficulty at times getting along, though they were largely still members in their local churches.
I was at that time questioning some Adventist beliefs before eventually leaving, but I was not in favor of the forum being split. The fundamental beliefs still define the official Adventist position. So I don't think it was good to divide the forum , and create a progressive one. The reality is they are all members of the same church, even if there is some variety of opinion. If the denomination won't draw a hard line regarding membership for those who reject particular doctrines, some conflict is inevitable on those lines.
And it was not something we saw much with other denominations, dividing them into traditional and liberal sections on the forum. It gives a negative first impression regarding Adventists overall to do so, in my view.
I think it was partly because the moderation was becoming very difficult, and some of the progressives were pushing for it as a means to say what they wanted.
The irony is that by the time they split some of the more vocal progressives had been banned for repeated violations. And when the two groups couldn't interact as much, the progressive forum was not that busy.
I would still be in favor of them simply rolling the progressive section back into the traditional and making it one Adventist section again.
