WAR is unreliable if it is used as an absolute measure. It is very useful as a rough indicator of a player's value. Whether you are into new stats, or prefer the more traditional ones, ALL stats are interlocked - they can't be used independently of other stats to form judgements. That is where WAR gets in trouble, imo. Too many fans misunderstand it and assume it is the ultimate measure of a player and they can ignore other stats. What's his WAR? Most fans on Redszone are more astute than that. WAR is just another number and formula to use in evaluation. If you depend on it as THE stat, then you'll get in dutch. As for the defensive metrics, they are vastly improved over what they were just 5 years ago - as they are harder to quantify, it stands to reason there are going to be some problems but computers and cameras are making it better and better - the eye meets the numbers so to speak.
One thing about Frazier/Bruce and WAR for instance - I don't like to measure WAR numbers of players at different positions - it's apples to oranges. RF comped to RFer, 3B to 3B, SS to SS. For instance in fangraphs calculation of WAR the difference in Runs is a swing of 10 in favor of the third baseman - which when you compare a third baseman to a RFer means that the solid 3rd base defender gets a fair boost in his WAR via defense which the RFer doesn't (the RFer is actually dunned -7.5 Runs). SS to RF has an even higher run value difference. If you don't understand this valuation by position you are bound to make erroneous judgements looking at WAR.