Academic / formal word meaning opposite of entrenched / set in stone
A leader board reflects changes in the rankings (by whatever means) of its underlying members, competitors, or components. Thus a good word would be
volatile
Subject to rapid and possibly unexpected change.
https://www.merriam-webster.com/dictionary/volatile
How about shifting? From M-W:
shift: to go through a change
Your example, slightly edited:
The market-share leaderboard is incrementally shifting.
The combination of incrementally and shifting conveys the impression that previously the leaderboard was not shifting, i.e., that the leaderboard was static or "entrenched".