I'd disagree with you, stranger - Jain Zar kicked no less than 5 Terminator armour-clad asses single-handed, given that no matter how powerful she is the body which hosts her spirit is still that of a female which is by default weaker than that of an eldar male. And she fought on unequal terms, wounded and surrounded. Accursed Talos killed her only through deception which was only to be expected from a scion of one of the most dishonorable and nefarious Traitor Legions - let it be known to everyone that Jain Zar is the coolest and most bad-ass Phoenix Lord who has ever trodden this bloody galaxy's space!
To be honest, a Phoenix lord is far, far more powerful than an Ork Warboss. HOWEVER, Phoenix lords are also in extremely limited number and aren't often on the battlefield. Warbosses are a dime a dozen, as they're regular orks who just fought a lot and are leading several squads of Orks. As a Warboss gains momentum, however, they grow very powerful. Only the "Unique" Warbosses, like Ghazghull Thraka, however, could ever hope to reach the same amount of power Phoenix Lords have. As someone mentioned earlier, the Phoenix Lords are pretty much demigods in their own right.
Remember that, as @Maensith says, no matter her body, Jain Zar still has the soul of a female, meaning she could never stand up to a masculine individual in any sort of straight fight. Since a well-educated and extremely reasonable board such as tumblr would immediately view any ork as a proper representative of the patriarchy, it is only natural that female Phoenix Lords will immediately crumble when faced with a warboss.
Terminator armor takes extra training for already elite units, she got bested by some mooks that'd never used them in combat nor trained with it before. Even sadder. Plus I think they removed it before the final battle.
You heretic! Jain Zair is best of the best, dont dare to disagree with this! She was wounded several times battling Terminators and thereafter, already tired, fought with 3 veterans at once - what more badassery do you need? I wish we had more such epic battles with the Phoenix Lords included, Dembski's battle choreography in the Void Stalker was incredibly cool
(Geez, I wonder what thread you read lately...) (Also, why would you start with a "I have read all GW books..."? I mean, you could bring in facts... But I guess we're going for the troll ^^)
Weird this thread hasn't been locked yet, wonder if one of the mods has a bias against a certain faction. These threads are pretty funny though, I like the trolling and other people coming in a being serious.