The Tank Commander can be a Warlord only so long as one of the other HQ selections is not on the table. But in reality, these HQs are the ones who are going to be spear-heading tank assaults on the battlefield and should be used as such.
Want to give one of your tanks a special rule? Then this is the person to do it. It will not die, as well as Tank hunters, Scout and Move through cover are all useful. Monster hunters is situational (but can be awesome if up against Tyranids). Precision shots and preferred enemy against infantry depends on the type of tank that the tank commander is occupying to be honest.
The increased BS on the tank is nothing to be sneezed at either. It really brings the chosen tank up to Space Marine standards, and with the special rules selected from the above, gives it a sound edge above them. It just depends exactly on the type of tank that they're selected to go with.
There are no builds for a tank commander, nor can they leave their vehicle. This means that they're not represented on the board. As such, they're just a tank upgrade and should be thought of, and played accordingly.
Take a tank commander or two on an important tank (especially a super heavy) and then put it to good use doing what it does best. Don't worry about other things - the Tank Commander is worth it for the right vehicle in the right situation with the right combination of tank weapon plus special rule.