I had a game vs new death guard about a week ago... I got clobbered by a fairly innocuous looking DG list. It was 2 units of PMs... one was geared up for CC the other was plasma+bolters, 1 rhino, foul blightspawn+stench vats, 2 casters, 1 LoC, 2 units of 10 poxwalkers, 2 hellbrutes(1 shooty 1 punchy), 2 PBCs (50 points undercosted imo), 1 bloatdrone with 2 spewers, 1 Miasmic Malignifer (aka, the fart factory). The mission was... 4 objectives and long deployment... I forget the name and I went second. So it was the worst possible army matchup with the worst possible mission using the least favourable deployment. That said, I do not think this matchup will be a fair fight until the WS get a new supplement that is brought into line with 9th edition mechanics in a similar manner to Dark Angels. The reason is that the WS core strength is HARD countered. You just dont get one of your army rules at all and there is nothing you can do about it.
I don't really have any non list construction solutions to this problem. DG is just gonna walk up to the midfield and you pretty much have to come to them since you won't win a fire fight before they are 50 points ahead on primary.
I think some things that might work are:
1. High quality 1 dmg weaponry.
-Redemptors dreads x 3 the best 170 points with the vehicle keyword in the codex. Everything else is laughably worse imo.
-Mario Karts in blobs of 3 if you can stomach the models.
-anything with lightning claws, VVs? Terminators... whatever. Bonus points for str 5.
-assault plasma hellblasters.
-blade guard vets... got spam? If you have 15 or are willing to buy/paint that many, I can't this being a bad option.
2. Mortal wound output.
-librarians... just use whatever powers do mortals... everything else is an optional extra.
-units that have mortal wound stratagems but are also not terrible. Hellfire rounds, meltabombs, whatever.
3. 3 Damage weaponry
-redemptor dreads, starting to see a pattern here?
-blade guard vets with doctrine active
-eradicators... obviously
-terminators with chainfists
4. Utility
-something that dishes out "can't fight until stone dead". Judiciar or the Whirlwind tank are both good options.
-a deepstrike threat to keep them from congesting in the midfield too much
-Kor'sarro Khan... +1 to wound is great vs t5
5. Allies. I hate this option but when you get hard countered by really annoying rules interactions sometimes you gotta comprise. Some good options...
-Guard vehicles. How about 2 tank commanders and 10 meatbags. You could leave 1 tank off the table to use use vengeance for cadia on whatever is close by. Bring your second tank on after the first tank dies and keep blasting. A demolisher with multimeltas will probably be best but I could see the punisher working also.
-Sisters. Not sure how exactly this army works other than miracle dice + meltas = stuff dies.
-Guard bodies. 610 points gives you 100 obsec bodies that a lot of DG lists will not be able to slice through all that easily. DG doesn't appear to have as much anti horde firepower as they do anti elite/tank. This is exploitable.
Here is the list I'm going to try in my DG rematch. It is somewhat constrained because I try to run lists using TTS based off of what I own.
Kor'sarro
Primaris Chap on Bike, master of sanctity, wise orator, exhortation of rage, canticle of hate, benediction of fury.
Incursors x 5
Incursors x 5
Intercessors x 5, ABRs, hammer
5 Bladeguards
5 terminators with chainfists
2 redemptor dreads with onslaught
6 bikers with 2 melta and a hammer
6 bikers with 2 melta and a hammer
3 ATVs with Multi meltas
I think this should do ok since it has enough dakka to hurt plaguemarines with shooting and enough low ap 3 dmg weapons in close combat to bypass the -1 damage. If I was inclined to purchase models purely for the purpose of drinking death guard tears I think I would drop all the bikes and add either 2 more units of bladeguard or 2 units of eradicators.