If the left wrist bends, the clubhead backs up because the left arm and shaft seeks the inline condition - a Physics fact. See Cochran & Stobbs, Jurgensen, Dr David Williams science based golf books.
Clubhead backs up? What does that mean? Clubhead slows down?
When left wrist is already extended a bit at impact, it just means its already past and has already sought the inline condition, like what the left wrist graph Brian posted. The Law of the Flail has already been done, satisfied. The "Physics fact" has already been satisfied. Does Physics say the inline condition must be maintained or kept, and prevent further uncock and roll of the left wrist?
In fact what you're saying is against the Law of the Flail because "trying" or actively flattening or bowing the left wrist will slow down the uncocking and rolling process of left wrist joint and therefore clubhead. That is why a flail's coupling joint is always a soft or loose material like a cowhide or "loosey-goosey" chain. "Harden" the coupling joint of the flail and you'll see it slows down substantially, almost becoming like a long stick, and will become useless as a flail. Might as well just get a long stick.
Again, FLW or ALW is just to adjust shaft lean and low point when your arc is small, which is what HK and BD has. A zeroed out accum 3 angle has very small arc, hence your AoA is steep and rate of closure very quick, hence clubhead goes down steeply, and goes up and left immediately. Clubhead travel for a given left wrist roll is substantially shorter. To compensate for these, you have to "delay" left wrist extension; otherwise the sweetspot will touch down too early and then go up and left immediately; hence the FLW concept.