So I'm midway through act 2 and came to the conclusion, that the templar is no help at all. Most of the time he uses the heals on himself because he just stands in plague/desecration and dies within seconds (it's hard to increase all resistances with only 4 item slots available). So the templar falls short of everything that could remotely be considered as support. Has anyone experience with other followers in inferno and their usefulness? If you found one particularly useful, what skills did you train them?
For me, the most useful follower in Inferno difficulty is the enchantress with the build Charm (charms an enemy), Powered Armor (15% armor buff), Erosion (extra 15% damage on an area) and Mass Control (AoE hex for 5 secs).
This helps with the additional disables (specially in Inferno), and she doesn't go in for the dive usually so she can help with some damage. One thing I've noticed is that when she sees an enemy mob coming, she always uses Mass Control, which is good, since you won't always be diving into mobs in Inferno.
You could also try swapping Powered Armor with Reflect Missiles.
Just to add I do find the Templar useful in boss battles though as a Barbarian. Usually he will die like you said but when he revives about 30 seconds later the first thing he does is heal you and then this repeats over and over again each time he dies.