Primaris
DC aren't a great datasheet but the firstborn are excellent and generally see lots of play in competitive lists. AoC +
FNP makes them fairly durable, they are cheap, and they have so many attacks. They also have their pregame move strat which is the only way outside of scout deploy units to force first turn pressure on your opponent.
Not being able to perform actions is a bigger headache than not being able to fall back in my experience.
LD 7 does suck for combat attrition but these guys are trade piece missiles, not objective holders.