You shouldn't be targetting through the tank, as most of the time they'll be cycling through targets to hold aggro, whereas DPS who aren't AOEing should be focussing fire on one target at a time. Plus, using macros for DPS abilities is bad anyway, as macros don't use the ability queuing system so you're introducing unnecessary lag into your rotation.

The only time you should consider using target-of-target abilities for damage is if you're playing a healer and you want to cast through the tank to help with DPS without losing your target for heals. Any other time, don't do it.