To be honest, I've had my engineer in maybe 4 or 5 battles now, and I don't think she's even been hit once, and yet was always a crucial part of the game. My plan with Teresa Dayo, is always to either plant a charge on one bridge (then back off 1 or 2 tiles) and immediately shoot it with an explosive bolt, or to use the 3x1 barrier ability to cordon off sections of the map to allow me to have strategic advantage, while she simply stays back after barriers are in place. The only time an engineer should even think about being near an enemy is if you are in total control of the battle and have no fear of them getting hit.
While assassins do have to get into the thick of battle, they can use Awareness to negate backstabs, and with their superior mobility, they can get into many situations where they have the upper hand. I tend not to use Tremolo very often though, since I rather try to stick with a more defensive formation in my strategies, rather than rushing forward.
