The easiest way to verify a defender's stats is through their attack. It is a set value, tied directly to PWR, and so as long as you can survive one hit you can learn a ton of information on what matters and what doesn't quite quickly. The only factors that matter to a defender are:
1) Power Score
2) Warden vs Non-Warden
3) Affinity
4) Defender Skill
5) Rage
A card's individual stats do not matter, those are all converted into PWR by a class-based calculation.
When it comes to serving as a defender your Attacker-class (Very High ATK, Low REC/HP) and Mage-class (High ATK/REC, Very Low HP) hero with identical PWR are likewise identical.
Wardens have a +50% bonus to this derived PWR score, and are built differently (when serving as GvG/PvP defenders they have lower ATK at a given PWR level, but higher HP).
Finally, Wardens have an undisplayed +50% bonus to relics power (as GvG/PvP defenders). So while in your GvG lineup a 1000 PWR Warden with 1000 PWR in relics will display as "2k PWR," they will have the stats of a Warden with 2500 PWR and 0 relics. This is why Wardens seem dramatically more powerful: exponential PWR means that secret 50% bonus makes them enormously stronger, even if they are much closer when you compare the true (rather than displayed) power scores.
Obviously, affinity, defender skills, and rage are on top of this. Leadership bonuses and such do nothing.
MTM Senior Member of the Forums