First of all, blaster attacks are „energy“ attacks. There is no resistance against those.
Secondly, the only kind of robot that will flee from combat is the lowliest Patrol-Unit (flees when cut to 40 HP from 400). So if you manage to lock on a Terminator, it should just go down (unless the other bots doing a „Brown motion“ accidentally get closer to you than the locked-on Terminator).
[ But in the result I do agree with you — there is no point in shooting Terminators like this since the others will probably take you down while you are trying to destroy one of them. And if you want to avoid that, you must play the game much more like a First-Person Shooter . ]