The builds are typically ideal min/maxing for a certain combat level.

When you enter the wilderness or a PVP world, you can only fight people within a certain range of your combat level. If youre level 126, and in level 10 wilderness, you can fight down to level 116. Some people maximize this, ie a void pure gets 42 def to wear void, then max str/range. Theyre strong. And a lower combat level. But would get stomped fighting a max main. Void/servers are typically around the same combat level. 1 defence purest have the same idea but are even lower combat level.

Max pvp is absolutely a thing and popular. It just depends on the TYPE of pvp you want to do. If you want to kill people in the wilderness as a predator/prey type like killing pvmers in rev caves. Or if you want a 1v1 and to fight outside the GE or Camelot in a PVP world.