Perhaps it’s the role you are trying to play doesn’t fit well with the Scrapper or it’s builds. I’ve gone for a sustain-tank that will engage on fights for brief periods of time – just enough to deny the opponent opportunities to focus my team.
The Engineer is a kind of support, the all-rounder. You should utilize your AoE buffs and interrupts to push teamfights your way. The Scrapper is amazing at chasing down those who flee as well – but if my team is there, I wanna be in the thick of it.
A personal and perhaps non-professional suggestion is try folding the elixir spec into your build. Elixir U breaks CC, and many traits allow you to pile on necessary buffs.
Alternatively, crit-builds can be amazing too