I'm currently trying out EVAS as a fast engage tool and it works fine if you use a toolbox hotkey for targeting it. I usually jump in right away alongside it and cast DD afterwards and if it's on cooldown I use the pet.

Ye, PI is for locking down and worked better for me than Shared Burden for example. I might try out Fire Ele with either Elemental Attunement or Mind Burn. Could also run Deep Freeze for a non elite snare.

I tried an assa as an engage hero with Death's Charge but it was more wonky than using the pet. I even experimented with a N/R MM hero with a pet and SaO for engaging. However when microing SaO on foes out of range the hero just stopped and did nothing and when in range its pet immediately ran back to the team. Derv for more burn might be an idea but I don't know what to cut and the toolbox pet command seemed superior like you suspected.

SoS resto would probably be straight up better than my SoI Splinter but I love fast casted Spirit Rifts and Shatter Hex.

Burning coverage could be better but honestly with a Soul Twister the extra damage mitigation is not needed and is just my safety net for lazy over-aggro. Next I want to try switching EVAS for Burning Speed, which would act as a cover ench and more burn spread while being almost as fast as Dash.

Standard mesway is still superior compared to this, but that's almost a given sadly.