You've pretty much perfectly hit the nail on the head here. This is exactly the problem with her writing.Let's look a bit at her personality, from start.
Warcraft 3: a proud warrior-priestess, leader of her race, letting nothing push her aside, not even Malfurion. She was much a "the end justifies the means" kind of person, which is why she freed Illidan, as the end (defeating the Legion) justified that and her killing some wardens. Quite an experienced fighter and commander, leading guerilla parties easily through a terrain she knows best.
War of the Ancients book (Knaak): a novice priestess in love with both Malfurion and Illidan, mostly Malfurion though. Damsell in distress, she fails time and time again at doing much of anything. She discovers having some healing powers and is promoted to High Priestess. Modest in nature and caring. This one is a bit out of the picture, as it happened 10k years ago, so might fit with personality. But then, you need to take to mind something, Tyrande wasn't young even then. Elves now live aroung 900-1100 years after no more Well, and if I remember right, she was already about 3k years at the Well of Eternity thing... so suddenly the young and a kind of Bella of Twilight Saga doesn't really fit her anymore, does it? This is one of the reason her description was critiqued so much there, he treated Malfurion, Tyrande and Illidan like teenagers.
Stormrage (Knaak): a warrior priestess, leader of her race, sent on a quest to save her beloved. Once again a "the end justifies the means" kind of person. However, not really a very experienced fighter, as she's pushed back several times by random orc lady and some other random creeps. After at start of story we hear how she trained every day, now she's defeated by every mob she encounters? So here the major lines were put well... but then she was made to look weak to make Malfurion look like the saviour... which made her look dumb. Especially that she fights with a glaive instead of a bow, though we know she's better with a bow.
Wolfheart (Knaak): a warrior priestess, leader of her race, letting nothing push her aside since she fought a larger enemy corps. Once again, an "the end justifies the means" person", as she thinks about burning the forest of Ashenvale because at least she'd kill the orcs then. She's here mostly as commander, and she kind of gets hit with an arrow. To kind of let Varian take the reigns as she can't lead anymore. So this is all a plot to bring Varian into the picture.
Her story: A caring mother who'd go to any lenght to save her adopted daughter. Until now it seems to fit the idea of a priestess and a caring person which was put forward in WC3 with her saving Malfurion and in Stormrage with her planning to save Malfurion. But wait... She comes there and almost dies... hold on... to be the damsell in distress and be saved by Malfurion... yea, ok. I don't think I need to say anything anymore.
MoP: A warrior, leader of her race, arrogant and full of herself, wanting to attack something head-on, exactly like the Horde said night elves are! Wait... haven't we been talking about guerilla warfare all along the other stories and her leading small groups in harassing enemies or trying to get an advantage (Malfurion, horn of waking druids, getting to World Tree first and letting everyone know, getting past demons, getting to Malfurion, getting to Well of Eternity etc.) So... where's that guerilla leader? The one who layed some traps and attacked and ran or had a distinct advantage before attacking in first place? Well it's there, it's called Varian.
How do I see the "true" Tyrande after all this?
-a warrior-priestess, with decisive decisions and yet caring for those close to her
-a commander of her people, a guerilla fighter, someone who fights from shadow or tries to get an advantage over the enemy before taking them
-an end justifies the means person, for whom victory is worth more then what is done along the way (kind of like Illidan here in a way)
-a ok archer (in no books or game is her shooting praised, however she prefers it to melee combat, which means she's better at it), but not a very good melee fighter which is why she trains a lot(in most melee confrontations she got defeated), and a good healer thanks to Elune(here is where she excels, and is able to use these powers as magic against her foes too with starfall wiping a full army of undead and so on), a good commander in setting up ambushes and carring them on.
-a person who might seem brash, but that's just because she's sure of herself and knows the goal.
Overall her strenghts are these: she's a good guerilla commander, a caring person, she's determined and amazing with the magic of Elune.
Her weaknesses are these: she's bad in melee(though she trains), she's a "the end justifies the means" person which puts her in line with many villans, she is unmoving in her decisions.
I made this using the descriptions along the books and such, removing the parts that were inconsistent from one book to another. Now if you look at that and compare it to how she was in-game... she was nothing like that.
-she was a bad commander, so one of her strenghts was turned to weakness, furthermore she forgat everything guerilla tactics
-she doesn't give a shit about anyone inside or outside the temple, once again, her caring gone
-she doesn't fight at all, so no comment on magic
-you might say she's still a "the end justifies the means" type of person... but no. You forgat that Tyrande only acted like that when the stakes were really high and didn't when they were not. This is why she focused on getting to Mount Hyjal when the stakes were high but left Illidan to run when Maiev was chasing him because they were not anymore, as she thought of Illidan as a sort of vigilante, bad by law but ok in general. Or why for example she fought the orcs and humans before the Medivh made them meet yet she accepted the Highbourne back even if her race had a quarrel with them.
In this case, the orcs were already in the temple, so they were already caught. The stakes were not high, so the end did not justify the means. She could have taken her time and made a trap or something, yet she did not... because Varian did it, because he was made to look better then her to justify Blizzard's wish of putting him High King.
And here is the problem.
I really wish they'd retcon all her new shit to match how she is supposed to be.