Raiding Tanks

[Bardo]

If you are a PLD and have already leveled CNJ to 34 for stoneskin and MRD to 26 for Mercy Stroke but haven't leveled anything else then I think the most logical answer would be to take Arcanist to 50.

You could level WHM from 34-50, but you'll want to level ACN to 34 for Eye for an eye and THM to 26 for Swiftcast. And that leaves you grinding out 76 levels to end up with just a Tank and a Healer class at 50.
If you level ACN to 50 and THM to 26 instead (and archer to 4, but that takes so little time it can be ignored), then suddenly for the same amount of EXP earned you have a Tank, a Healer, AND a ranged DD class at 50.



*however it looks like you already have BRD at 50?
Being able to swap to BRD should already handle the vast majority of situations where you want to swap a tank out for another class.
It's almost always better to take an extra DD than an extra healer in those single tank situations.

So in your specific situation, I wouldn't worry about leveling anything else unless you just hate BRD or really find yourself enjoying another class.