One of the faster DRs on our shard (Jan 2017) runs with SiM in place of SiT, so it's possible to run without him (but this has Malak). In mirrors you really want your BSF to go before their BSF. It's unfortunate, but many mirrors are determined by who resists the first CBM.
If you don't have SiT, you can consider KRU for mirrors. I'm not sure what, if any, value that brings to JKR matches. I have an account that's had DR / Malak since release and a second which unlocked him yesterday and at G10 he was having a hard time with arena caliber JKRs - was actually much easier to climb with JKR, but I was also using Sion / Thrawn instead of DN so there's that.
Malak makes the DR team significantly better.