This is the reason why Defence, Hitpoints, and prayer skills are generally the ones with a more basic. It's hard to know what skills are the RS gold least important, so it's up to player preferences on which skills to limit and which ones to maximize. While deciding, keep in mind that the lower your level is, the more easily enemies you will be able to take on, and thus, the more successful you will be.
In terms of the most under-reported stat, it is usually Defence and isn't necessary to play PVP. The greater the threat's Defence levels, the less the likelihood of landing an effective attack on him. But, it doesn't decrease the amount of damage you'll be able to cause. This is also the reason for your ability to wear protective gear. You can't wear a high-quality armour or helmet without meeting the Defence level requirement. It's the most crucial aspect as better equipment will decrease the amount of damage that you sustain.
Then why is Defence less important than the abilities that deal with damage? It's because, aside from defence, you possess the Hit Points attribute that determines how much health you possess. If your health points are very high it is possible to cheap OSRS gold survive a lot even with the initial level of defence skill. With a decent level in your primary combat skill (either Attack, Magic, or Ranged) You will be able to finish your opponent prior to him finishing you.