Well, let's compare the Wraithlord to the other Toughness-based Dreadnought equivalent: The Carnifex.
Advantages of...
The Carnifex:
-More options; perhaps the most useful being Extended Carapace.
-2d6 Penetration dice in close combat
-Higher Strength ranged weapons
-1 more Wound
-5 points cheaper
-Implant Attack is good if you match up against a Wraithlord, but against other things, auto-kill usually makes it redundant.
The Wraithlord
-Higher WS (+1) , BS (+2), S (+1), T (+2), I (+3), and A (+1) (Carnifex could take Scything Talons, but would bring cost over 75. Other upgrades would similarily increase cost)
-More ranged weapons, with better AP, accuracy, # fired and range
-No Shoot the Big Ones
-A Starcannon against a Carnifex is far more effective than a Venom Cannon against a Wraithlord.
Personally, I'd rather have the Wraithlord. I think the Carnifex is just as essential to the Tyranids as the Wraithlord is to the Eldar.
Rending Claws vs. Wraithlord: A Genestealer's attack will wound 1/9 times against a Wraithlord. Discounting morale and chargin bonuses, the break-even point is:
2 x 1/9 Genestealers per 1.25 Wraithlords x (3 - 2 x 1/9 Genestealers) / 3
Plugging in 1 Wraithlord we end up with 3.97 Genestealers per Wraithlord. This is 63-64 points. From this, it may appear that the Wraithlord is at a disadvantage. However, this only covers the melee aspect.
With its twin Flamers, and at 75 points, do you think a Wraithlord, on average, will be able to take out even ONE Genestealer before they get into melee? I think so; with its auto-hit and penetration, a Genestealer under each template would generate 1 kill on average. 3.97 + 1 dead Genestealer is 79-80 points, more than the Wraithlord.
Now, moving onto the heavy weapons, which Wraithlords MUST take now:
A Shuriken Cannon costs another 25 points. Do you think it can kill two Genestealers (32 points)?
If a Shuriken Cannon can do it, so can a Scatter Laser.
There is no reason to take a Bright Lance against Tyranids, unless you are crazy about that auto-kill. Even if you do, you'll most likely be able to slay three before they get to you.
The Starcannon, with its longer range, will be able to take another one down over the Shuriken Cannon.
The EML... a Plasma missile at its range will easily slay four Genestealers.
As for the Genestealers' upgrades... sure, Implant Attack will be useful against a Wraithlord, but it reduces the number of Genestealers, and it won't save them from the Wraithlord's guns. Plus, it really isn't that good against anything else. In any case, with it, the break even point is:
2 x 1/9 x 2 Genestealers per 1.25 Wraithlords x (3 - 2 x 1/9 x 2 Genestealers) / 3
Or 1.99 Genestealers. This is nearly 40 points, meaning that two Genestealer kills from flamers will make it even.
All things considered, the Genestealer is just about the ideal thing to take against a Wraithlord. If they only deliver this kind of performance against a Wraithlord, then I think something needs to be changed slightly.