A few years ago / until a few years ago [closed]
Solution 1:
Until = “up to (the time that)”
Cambridge dictionary
All we know for sure from this sentence is that During a period that ended at the time that was a few years ago, the model prevailed. The implication is that at that time something changed so that the model no longer prevailed. In normal usage the implication would be confirmed (or denied) by either or both of the preceding or following statements.
If until is removed, the sentence states that At or around that time that was a few years ago, the model prevailed. It tells us nothing else. As above, there may be an implication that other models prevailed before or after that time, but these implications may only be confirmed (or denied) by preceding or following statements.