First I want to say that I do not know anything about the fluff so you have to excuse me for that.
The thing I see first is a part of the Vigilus book which I strongly suggest you get.
Swap all the
HQ so lord discordant is with maulerfiends.
Pay 1cp to make the spearhead “soulforged”. All engines and Warpsmiths gain this keyword.
Pay 1cp for “field commander” for a Lord Discordant to get a second
WL trait. Then give him the special trait so he gets a 6” aura and gives + 2” move too all engines and Warpsmiths.
You get a stratagem for 1cp so you can advance and charge with an engine. If you want you can make one lord “khorne “ and buy the relic “talisman of burning blood” for advanced and charge and then warptime a third engine to possibly have 3 big stuff in enemy face turn 1.
As you said yourself, drop MoP for more havocs with reaper chaincannon for more shooting at screen so your engines and lords make it to combat with the juicy stuff.
Sorry my bad explanation and grammar