If the idea is that handicaps may be wrong because of the players’ rating fluctuates too much (randomly suggesting too high or too low handicaps), then this fluctuation itself could be looked at.
For example, compare rank graphs of this server to other servers (only players with hundreds of recent games oc). If lines tend to be smoother elsewhere (for similar levels) then ratings here are likely inaccurate (random-noisy) as hypothetised. (Another test is how much 10 game streaks move already-solid ranks.)
A player may play better one week than the other, but this is exactly what a rating system should NOT try to follow (same noise like in a single game he may play better than the next game - yet ratings average over hundreds of games for good reason).