On rs3 I guess pure builds are ruined since eoc.
On oldschool I have a 1 defence pure, the most common of pures and also a defence pure which are accounts with 1 attack, strength, magic and ranged, optional 1 prayer or not and high defence, the propose is to hit 75 defence for the dragonfire shield and serpentine helm, the shield hits up to 25 with the fire and the helm causes the opponent to get venomed which is a stronger form of poison which starts to damage 6 and goes up 2 damage every minute or so up to 20 damaged. They are optimal for armour stakes and fighting obby maulers.
My 1 defence pure is self sufficient, my defence pure is not at the moment but I can easily make it self sufficient if I have the patience to get some profitable skill high enough like runecrafting or hunter or mining etc.