A bit of World PvP advice from a veteran MMO player
I love world PvP in games. It lets player's make their own stories and rivalries rather than relying on some piece of generic lore to justify their actions. Over the years I've played alot of games with world pvp; GW2, WoW, Warhammer Online, and EVE to name a few. Some of them were good, some of them were bad, but out of all of them I think the game that implemented world pvp the best had to be Warhammer online.
From Warhammer's launch World PvP was considered the core content of the game with PvE being an important but minor and ultimately optional part of the game. The game delivered on that end. The PvP was fun, the classes were interesting and diverse, and the PvE took what was then a radical shift by having many of the quests be open world public quests, which people seemed to enjoy.
In many ways Warhammer online was set to be the next big MMO but after a few months over half the initial players quit the game and it led to a slow and ultimately irreversible death spiral. The problem, from the point of view of someone experiencing it, was two fold; lag and lack of end game content.
Warhammer online was released early with much of the end game content still under development. A major feature of it's world PvP system was the ability to capture castles and besiege the enemies home fortress, but therein lied the problem. With hundreds, sometimes thousands of people fighting and casting spells on both sides of the battle in a tight cramped space like a fortress hallway a single action sometimes took minutes to register in the game. It became impossible to capture a fortress in the early months simply because the attacking side would lag too much to kill the defenders.
On the other side of that problem was the content. After you managed to besiege a fortress the hypothetical goal would be to attack the enemy factions capital in an instanced raid vs raid mixed PvE/PvP battle that often pitted guilds on opposing factions against each other. This was great fun, gave great loot, and lead to alot of forum drama. The only problem was it was implemented months after the vast majority of the player base had already left. To make matters worse alot of guilds would push city raids at 3 in the morning to avoid competition from the other side and collect the rewards uncontested.
Alot of these problems seem to be known to the ashes of creation development team and I'm glad that they're taking them seriously. You can't have a game with mass world pvp, or even instanced mass pvp, and have it turn into a slideshow. It will kill the game before it even starts. I'm glad that they're making city captures only happen during prime times, this fixes the problem of guilds pushing content at 3 in the morning to avoid competition.
However, there is at least one suggestion I'd like to make that could help improve world PvP in this game. World PvP is inherently asymmetrical. One side could bring 8 players and the other 20. One side can be a close group of friends all in voice chat, the other a pick up group loosely tied together for a single goal. This is part of the fun of it. However, another flaw in warhammer online was unfortunately how asymmetrical it was. After a while servers would develop faction majorities wherein one side was 70% of the total population and the other side 30%. When this happened that differential would increase over time. Eventually the skew was so bad that the remaining players on the minority faction would just quit the game or move to a different server rather than fight 10 vs 1 any time they walked into a world pvp zone. It was demotivating and would kill servers as once the minority faction was effectively wiped out the majority faction would have nothing to do and quit as well.
The fix to this is incentivizing the minority faction to play when they're out numbered. In ashes of creation you don't seem to have real factions but you do have guilds which will control castles. Eventually there will be situations wherein a large guild with many players will be at war with a small guild that has less than half their number. It could well turn out that in these cases the smaller guild will simply be too demotivated to put up a defense. Fighting 150 players vs 500 will lead to a loss 99% of the time. Motivate them to fight even if they'll lose. Give the outnumbered guild a special bonus for fighting against the odds whether it's a scalable exp buff while in the instance, an extra item reward for fighting 2x or 3x their numbers, protection from looting on their ingame house, just something tangible that will motivate people to play even if they'll lose.
Imagine corralling 500 players to siege a city and when you show up it has 10 defenders. That's not fun for either side. Incentivizing defense of a city either by the guild that owns it or by random players unconnected to the conflict will vastly improve city sieges and help stop them from being a one sided stomp.