Engagement metrics measure interaction rather than exposure. Dwell time, touches, completion rate and the point in a video where viewers leave all require the audience to do something, which makes them a stronger signal than "the screen was on and people were nearby".
Interactive video is where they become genuinely rich, because every session produces a path rather than a view. Knowing that most viewers abandon at the same question tells you exactly what to fix, which an impression count never does.
The caveat is that engagement is a proxy for value, not value itself, and optimising the proxy is how campaigns go wrong. Content can be made stickier in ways that do not sell anything: a longer path, a more compelling but irrelevant question, a game people play instead of buying.
Pick the two or three metrics that plausibly precede the outcome you want and ignore the rest. A dashboard with fourteen engagement numbers is usually a dashboard nobody has connected to a decision.