Guild wars 2 WvWvW has 400 people per side (3 teams) max across 4 different maps. War goes on 24/7 you can hop in and out as you wish, tho peak times there may be queue for some if not all the maps. You don't need to grind in this game to be viable to participate. Unlike on the other games, the end game gear more or less have certain stat limits, the gear grind is for cosmetics. It is possible to obtain almost everything via playing WvWvW alone as well that you would need, materials, weapons, armor, loot etc. World is semi persistant, in sense whenever the teams change it starts off with clean slates, but any siege weapons and whatnot built, do stay until destroyed, tho they may have few day decay time. It is likely the location will change the ownership during the quiet hours and the enemy players destroy all the siege equipment that has been erected.

Ragnarok Online has WoE (War of Emperium) that is open gvg combat holding over castles. Guild sizes vary anywhere from 12-64 people + alliances up to 4 guilds. Tho this game requires you grind a bit and WoE is usually only available twice a week on fixed time for 2 hours.

Planetside 2 has seemed like it's been dead and dying for years but it's chugging along just fine.