Need help against guard + knights

Hello.

My main opponent plays Imperial Guard - mostly mech, but sometimes a blob is also used. Recently two Imperial Knights were added to the list, so currently it looks something like this:

2 leman russ exterminators (autocannon ones) - squadron with tank commander
2 melta stormtroopers in tarox primes (taurox battlecannon with twin-linked autocannon)
2 melta veterans in chimera
2 wyverns
2 imperial knights with melta cannons

Sometimes stormtroopers and 1 wyvern are dropped, and their points are used to buy some guardsmen with autocannons, including company command squad in chimera (so, ignore cover order)

We mostly play maelstrom.

My list is usually some variant of a skimmer spam: something along the lines of 4 venoms, 4 raiders, 3 ravagers, 2 razorwings. Passengers in transport have blasters (trueborn have multiples, of course).

Currently I am unable to deal with these guard lists. It surely may have something to do with my skill as a dark eldar player, but I don't even know how I can improve in this way. I try to hide my skimmers behind terrain - and I should note that we have a good quantity of terrain on table (usually it is ruins) - but it doesn't really save all of them. Last 4 games saw most of my army dead in turn 2. My firepower is not enough to destroy a good amount of vehicles a turn - not even talking about knights. On the other hand, any lucky penetrating hit can destroy any of my skimmers. And wyverns are brutal to anything not in transport.

What approach can I take to improve my list and/or playstyle?

I play Guard a lot, so I know your pain. 2 units of Scourges would go a long way to take out some armor. Its much naysayed on the forum but WWP Archon and deepstriking Blaster Born would be necessity in this list as well. Fire Dragons or Wraithguard would be much better if you ally. I think you need to capitalize on deepstrike ability of the army to avoid having to push up the board against all that firepower. There are a lot of twin-linked autocannons in his list but lanced up Razorwings should be good to go after your deepstrikers do their work. A blaster in every warrior squad would be good too.

Playstyle wise you gotta pop those tanks and just play to the mission. If you're playing Maelstrom DE speed is a big edge.

Thank you for your reply.
I'd like to keep my list as TAC, so I am not sure about scourges. Tyranids and tau really like me spending points on haywire instead of poison/lances. Also, my concern with them is that they only have 1 turn to do something useful - next turn they will be eaten by wyverns or heavy flamers. Also, there is an issue with them (and with WWP guided deep strikes as well): they do not come until turn 2, they do not come turn 2 reliably, and they diminish my effective output and board presence (hello, maelstrom objectives) until they come. And, by the way, blasterborn can semi-reliably kill one vehicle - as long as that vehicle is not an imperial knight =). I know about the trick with placing raider in a way that it covers 2 facings, but I assume that knight will cover it's back with the shield, so it is either 4+ saves or 4 to glance, 5+ to pen. Don't see them one-shotting a knight statistically.
I am open to allies, but what really should I take? Fire dragons are nice, but as long as I use allied detachment I can only take one of them. We play LVO-style rules, as they seem to be more or less balanced, so two sources. I can go eldar CAD + realspace raiders, but I am afraid that it will soon turn into something like eldar + 1-2 archons with WWP and 80 points of kabalites and maybe a couple of raiders for dragons to ride in.
Not that I rule out this possibility, but I'd like to know what other options I have.
And yes, every warrior squad has blasters.

His list looks like it was made specifically to eat our flimsy paper plane transports. So take away what his army does best by using Coven formations and WWP. A Corpsethief Claw with HL or HWB, Dark Artisan, and Grot bombs/Grotesquerie WWPing down in his backfield will make short work of the Wyverns and anything with rear AV 10-11. The Corpsethief and DA support one another and draw the attention of the Knights while your Grots squads wreak havoc.

Well, first of all it's two sources, so this approach does not seem to be possible.
Second, I am effectively giving two turns of uncontested grabbing of maelstrom objectives.
Third, I don't really think knights would concentrate on slow-moving taloses instead of immediate thread in form of grotesques. Also, it would seem to me that knight statistically has more chances to kill a bunch of taloses than vice versa.
And fourth, grotesques can't really assault the turn they deep strike. So, deep strike, get shot out of transports, get burnt by heavy flamers, melta, wyverns and/or get charged by knights.

Am I missing something?

You didn't mention a tournament two source restriction in your original post.

If you place your objectives smartly then you partially mitigate the maelstrom issue.

TL HWB or HL + S10 Smash attacks can be bad news for a Knight. I've used them to great effect against Knights thus far. If he ignores them, then let the Talos rampage around collecting VPs with every unit they kill in assault.

Grot bomb = large 7-10 man units of Grots + WWP Haemie. You place them wherever you want, to include somewhere in cover or BLOS terrain to minimize incoming fire after they land. A large Grot squad can easily shrug off flamers, melta, and Wyverns as even if a few die, 5-6 are still more than capable of handling IG in assault.

I'll refer you to Mushkilla's Repugnant Rambler battle reports in the Realspace Raids forum. I've been running something similar to Mush with great results. If what you're doing isn't working, don't be afraid to try something new.

Mech guard can be a problem for DE.

It is tougher than we are, has more guns, and there's a lot of it! Our AT shooting gets overwhelmed. If you trade shots with them, even when ur in cover, you will suffer.

What has worked well for me vs mech guard + knights is...

-The mission is all there is, ur entire army is expendable.
-Get as much LOSB terrain on the table as possible.
-Try a WWP bomb or 2, firedragons for anti-knight and/or grots for anti-backfield/artillery.
-Taking fast MSU for the rest of your army helps with maelstrom.
-If you cant deploy a unit behind LOSB terrain reserve it, Autarch for reserve manipulation.
-Hide, don't trade shots with him unless he cannot shoot back with many units.
-Don't fight his whole army, use terrain to break it up, overwhelm it one piece at a time.
-When WWP bomb and other reserves arrive swarm the flank that has the most terrain to shield you from a lot of his return fire.
-Target his fast obj grabbing units when you get the chance.
-The mission is all there is, your entire army is expendable.

As sweetbacon said a super tough covens list might cause him some trouble too.