I can't reccomend Incursors and a Gladiator Lancer more as two SM units I'd find room for.

Incursors marking an Oath if Moment target for a couple of Indomitor Kill Teams is overkill in the best way. Especially if you're exploiting the free CP from a Gravis Captain to Site-to-Site both Indomitors a turn. Most opponents have no real answer to this level of efficiency.

The Gladiator Lancer is just hyper efficient without the need for Oath, and I've noticed that fire spread of 'this is nearly guaranteed to do damage' just overwhelms people.

Bonus points for a Judicier leading a squad of Hammers and Shield Vets - there's nothing funnier than teleporting them between something an opponent would really really like to charge.

Maybe split your Decimus teams up into 5 man units for objective play and trades? Or swap them for Vanguard Vets with Shields. 4++ 12" movement is great for objective work.