Dark Elves can be a top tier army, second only to Lizardmen, in a general gaming environment that is not strictly comped but also does not allow special characters. You really need at least 2400 points and preferrably 2500 points to run the optimal build with with pendant dreadlord and the lvl 4 sorceress with sac dagger, lore of shadows combo.
Hydras are vastly under-costed and one of the most potent and effective units in the game. The regen and armour save plus T5 makes them harder to kill by shooting (unless a flaming cannon ball). They get 6 attacks with hatred at WS 4, I5, S3 with AP from the two handlers (who cannot be targeted) and 7 attacks with hatred at WS 4 and S5 (I2) as a base in every round of combat. The monster causes terror (chance of a failed fear test or terror test nerfing the ability of the opposing unit to fight or to stand fast). In close combat, once per game the hydra gets a breath weapon attack with S = remaining wounds (2D6 hits in combat) and gets a thunderstomp against standard infantry and war beasts. It is one of the few models in the game that can solo charge a horde unit or harder unit and kill so many troops and hold up so well that it will more often win and so deplete the unit that it will be devastated even if the hydra dies (killed chaos marauder, grave guard, tomb guard, flaggelant, greatsword, and bloodletter hordes and ogres and ironguts with single or double hydra charges in multiple turns). I've also charged a hydra into a unit with lower I and focused on killing a key character, even if the hydra ultimately dies.
The dreadlord can be run on the peg with crown of command, pendant of khaleth, with possibly dragonhelm (ward save to flaming and +1 AS is important to deal with metal lore spells) and possibly consider whip of agony or soul render. This model can be very vulnerable to lore of metal and lore of death and certain other spells that do not have a stength value or have low strength values and, yet, can get by the high armour save. Also, I have sometimes played him too recklessly. He can often hold up a really tough unit and kill out the characters or wear it down but he will fail one out of six LD break tests, so keeping the BSB nearby is important. Also, he can be run within range of harpies to boost their LD (which is very low) and allow them to get into attacking war machines and diverting units.
The alternative build for the dreadlord is on a cold one mount in a decent sized unit of cold one cav (typically with the BSB in or nearby to minimize stupidity test risks). I played this variant quite successfully in tournaments using the magic item allowance on the champ to boost the unit and the Banner of Hag Grief (ASF to the unit) with the dreadlord having the whip of agony (+1 attack, AP, unmodifiable S5 attacks). The cold one easily gets a dreadlord with the whip to a 1+ AS (+2 for mount, +1 cloak, +2 heavy armour, +1 shield). Also, it is more difficult to snipe the dreadlord in that unit. Even with the 5+ ward save blessing of a cauldron, I find that the cold one knights with T3 and 2+ AS will often eventually be killed off, but they will last long enough to get the dreadlord more safely and with fewer break tests into effective combat and can kill enough of the opposing unit (especially characters) to earn their points. The COK unit works well with the hydras supporting each other. If your mage has lore of shadow and miasma's (use the boosted 10 version to nerf both I and WS) on the opposing unit, then with the ASF banner the riders, dreadlord and sometimes even the cold one mounts (S4 T4) will get to re-roll to hit against most opposing models and often the opposing models with be rolling to hit on 5's instead of 4" (atack least against the dreadlord).
Bolt throwers are not great in 8th edition. They only have two wounds and BS shooting is disadvantaged and must really be effective to earn their points.
The best BS shooting in the game is from repeater crossbowmen (with shields amd musicians justified) due to high BS, 2 shots and move and shoot abilities with AP.
I find corsairs to be fun but not all that worthwhile other than as a screening unit (screen balck guard unit from shooting). They can tear through light infantry but will struggle against more elite infantry with their S3 and T3. One unit with the frenzy banner (serpeant banner) is the most I would play. You lose the multiple attacks from the supporting ranks your are paying for. I've run a screening unit with repeater handbows because it gets multiple shots from the second rank and has quick to fire.
I've found witch elves with the banner of murder and a cauldron to be more effective (more attacks, stubborn, frenzy and poison). I've found black guard are vulnerable to shooting and magic and struggle with modest armour saves and elf toughness T3 but their stubborn ability, immune to psych, multiple attacks with halberds and re-roll to hit abilities can make then a nasty unit if successfully screened and delivered into combat. I've often used a cauldron's 5+ ward save on this unit to allow it to survive longer.
Finally, a lvl4 supreme sorceress with a sac dagger is one of the best offensive magic users in the game. I play her with shadow in a large spearman unit with standard of discipline (boosts LD to 10). You get to roll the dice and, if you fall short or don't roll a 6, you can boost the casting value by killing one cheap spearman and roll another die. One way to put pressure on the opponent, is to roll one die at power of darkness (produces 1+D3 power dice for the sorceress) and if yes roll a 1 or 2 use the sac dagger to roll a second die. Then immediately use the additional power dice gained if the spell goes off to cast something of value. The opponent either lets the power of darkness spell go off and is then at a disadvantage throughout the remainder of the magic phase or uses up dispel dice (most often at least 2 and often 3, or even a scroll) which leaves you with more of an advantage the remainder of the magic phase. The sac dagger allows you to use one fewer dice in some casting attempts which cumulatively reduces the miscast risk and you can then boost it accordingly.
Another favorite model is a master with cloak of hag grief (+1 AS to shooting and cuts all ranged attack S in half rounded up) on either a peg or dark rider. The peg's three wounds is worthwhile, if you can afford it, because it gives the master three wounds, instead of two. Then either run dawnstone (re-roll armour save) if facing war machine and shooting heavy armies or ring of hotek (causes miscasts on doubles rolled by any mages within range). He makes a fabulous war machine hunter, redirector, can take out fast cav and lighter scout and skirmish units, and with the ring get totally shut down or wreck a magic heavy army if he can safely get within range. In fact, he can be so annoying that the opposing army will spend so much time trying to kill him the rest of your army can get in and do damage. It takes a lot of skill to use him and play "hop-scotch" by flying around behind enemy lines to force the units with mages to move around and avoid the ring. The biggest risk is forgetting to ensure that you casters are not within range of the ring.
The thing is that the dark elf army has many options and is challenging to play and, yet, highly competitive. Unfortunately, ETC took a lot of the fun out the army if the currently proposed restrictions are applied. Dark Elves in a lightly comped or non-comped environment (our Indy GTs) are above average but are not winning at such a high percentage that they are broken, unbeatable or unfair. Only Lizardmen are clearly advantaged in 8th edition in a non-comped or lightly comped environment. (If allowed lord level special characters, High Elves and Daemons of Chaos can be close to unfair or unfair, especially with no restrictions on unit sizes in buildings and folding fortresses for high elves. )