it is stupidly effective.
the whole "Assaults are king" in 5th is overrated BS spewed by morons who dont know how to play.
the DE work well as an assault army, using and abusing Wytches as hold up units, so long as they have FnP they are impossibly hard to kill in close combat, needing to get through 2 4+ saves, as long as your not facing FNP ignoring weapons.
but Ive said it before in other places ive given advice, DE are BETTER at a range.
think about it:
I have 10 Vehicle targets on the field, each being easy to kill, but so cheap, point wise, that i can easily afford to lose them and still go on to dominate in my next turn, most armies would end up with, approximately 4? units dedicated to Anti Tank. outside of Leafblower IG, and Razorspam SM lists. because of this, they cant deal with the stupid mass of vehicles I have before I rip through their units. having 4 blasters into one transport, 5 into another, then having 72 shots from my Venoms into the squads, will annihilate their assaulting force, add to that i have a single wytch squad i use as my hold up unit, to try and keep units i dont want near my vehicles, just out of reach for a turn so i can turbo boost, or move 12" away to save the vehicles.
One thing I say to EVERY new DE player, and now im saying it to you, FOCUS your attacks and abuse Line of Sight. If your getting a cover save from an opponent, your playing correctly. if your focusing down one unit at a time, your playing correctly.
if you spread out your attacks, you lose, if you focus your attacks to bring targets to the points they need to be at (IE: preventing transports with big cargo, Land raiders, to not be able to move = good. Destroying heavy weapons / wrecking Anti tank vehicles = good)
The reason my list works well for me is I abuse Line of Sight, making so Im either untargetable or I get a 4+ cover on my vehicles from units Im not destroying. add to the fact I make sure to have many targets for my opponent to wrack his brain over on which ones to target, gives my army an edge over all but the two lists I mentioned above, which work in a similar way.
and for the record, it is 'a whole load of guys shooting from flimsy transports' but when you have amassed as much fire power as my list does, losing a transport or two, does not seem like a huge loss (if you notice, my units are 125 points a piece more or less, in a 1500 list, thats nothing if i lose a part of the squad)