I never quite got why PoW makes one possible chain more valid than others? Comparing chains would make it possible to track it back to the divergence, right? And aren't there timestamps in place that can then determine which chain was 'diverged' last, hence would be the copy?
Nodes will always want to follow the chain with the largest proof of work. By doing so, it ensures that an attacker cannot broadcast a different chain with a significantly lower Proof Of Work (ie. Much lesser efforts) that replaces the transactions in the chain with the largest PoW.
Timestamps are not followed strictly within Bitcoin and there is a fairly big deviation allowed from the median time. I'm not really sure what you mean by tracing the divergence or how it'll help in this case?