The more different types of attackers a deck has, the harder it becomes to get the right energy at the right moment
Yet as I opened an Elite Trainer Box, a Booster Bundle, and an Alakazam ex box (very kindly provided by TPCi), for a total of 20 packs, I saw so few of them

Sheoldred, Whispering One EDH Creature (27) 1x Avatar of Woe 1x Blood Artist 1x Butcher of Malakir 1x Chancellor of the Dross 1x Dark Impostor 1x Deathgreeter 1x Desecration Demon 1x Geralf's Messenger 1x Geth, Lord of the Vault 1x Harvester of Souls 1x Helldozer 1x Kokusho, the Evening Star 1x Massacre Wurm 1x Mikaeus, the Unhallowed 1x Mortivore 1x Necropolis Regent 1x Nether Traitor 1x Nirkana Revenant 1x Pawn of Ulamog 1x Phyrexian Obliterator 1x Royal Assassin 1x Sangromancer 1x Skirsdag High Priest 1x Solemn Simulacrum 1x Vengeful Pharaoh 1x Wall of Souls 1x Wurmcoil Engine Planeswalker (2) Land (36) Enchantment (11) 1x Bloodchief Ascension 1x Contaminated Ground 1x Contamination 1x Exquisite Blood 1x Grave Betrayal 1x Grave Pact 1x Heartless Summoning 1x Painful Quandary 1x Sanguine Bond 1x Underworld Dreams 1x Wound Reflection Artifact (6) 1x Altar of Shadows 1x Grimoire of the Dead 1x Lashwrithe 1x Scythe of the Wretched 1x Sensei's Divining Top 1x Sol Ring Instant (6) Sorcery (10) 1x Army of the Damned 1x Beacon of Unrest 1x Damnation 1x Diabolic Revelation 1x Exsanguinate 1x Mutilate 1x Promise of Power 1x Rise from the Grave 1x Sadistic Sacrament 1x Temporal Extortion

It doesnt do much immediately, but it sets up an explosive follow-up, allowing you to storm again or refill your hand
The deck will still have legs, especially if you replace them with more combat-oriented slivers like Spiteful Sliver or more recursion like Dregscape Sliver
Once you have enough mana to do everything you want to do, extra lands can become dead cards they no longer impact the game at all