From my experiences playing, from what others have said, and from what the current meta is - I would avoid taking a pure DE list for competitive play, but they can very easily compete with your local groups armies unless everyone is min-maxing or just playing blue smurfmarines.
With your army below:
Your archon is crazy expensive, do you want to be in combat or do you want to shoot? The blaster is great, but why take it if you're taking a cc loadout? huskblade sucks and the nade launcher is pointless as it doesn't affect marines or fearless units.
The court with sslyth are great, but putting 300+ points in one basket and charging up the middle will result in simply losing said 300 points to basically any army that can shoot - does your archon waste his blaster shot on infantry, or are your carbines wasted against vehicles?
Trueborn are good but again, are going to be a target, and blowing a venom up isn't hard, bolters do it just fine, jetbikes with a blaster and caltrops, scourges with haywire, ravagers etc do it better, cheaper and safer.
Gunboat Raiders with 10 kabs and a cannon was a thing, with the new faq draft and how it relates to units snap firing after their transport jinks, snap firing if you move more than 6" and splinter cannons firing less and at a shorter range b/c of salvo. They're not going to do much IF they survive getting close enough to actually make use of the splinter racks, you don't want be in rapid fire range as your unit = dead against basically anything that can shoot.
Scourges are good, basically either take haywire and possibly take potshots from deployment or heatlance and suicide them in. There is literally no reason to ever take splinter cannons and or a squad of 10, we're not space marines.
Lance ravager's are alright, however, with little redundancy - 3 lance shots hitting on 3's, glancing on 4's vs av12 and with most competent players using cover, probably not effective, i would take 2 or even 3.
You really want lots of small units, we don't do large blobs well as 5+ with a 6/5+ fnp @ t3 isn't going to keep you alive against much, venoms always take the cannon upgrade as they are the best and most reliable source of survivable poison shooting.
Ditch trueborn, take msu squads with blasters, make the enemy work to remove the threat, not just shoot at one unit.
eg just messing around with stuff but something like this would hold up better:
lhamean + 4 sslyth in a venom w/cannon (175)
3 x 5 kabs with a blaster in a venom w/cannon (360)
1 x 5 Scourges with haywire blasters (120)
Ravager w/3 lances(125)
Your hq unit now has a single role, shoot stuff, you have 6 obj secured units, 4 venoms to shoot infantry and your kabs can multirole and or hunt MC's or take potshots at vehicles, scourges can sit in cover and zone or deepstrike and attempt to remove something. Your ravager can sit backfield and shoot.
This comes to 780pts, i would add a second ravager and maybe a 3man reaver unit with a blaster and caltrops.
Please excuse awful spelling, punctuation and generally bad sentences