This is my take on it.
Pros.
no more ♥♥♥♥ing towers. a 15x15 is the minimum requirement to make unraidable towers. having the central tower as a 15x15 from bedrock to sky limit and then building a claimed wall around it effectively a 45x45 perimeter wall would make it so that u have to dig out enough keys (LCBs)from the perimeter wall in order to be able to place wood frames near the tower. you would want keys on the edges of the tower so that u can only place blocks 7 blocks away from the tower. this makes it so you protect your tower walls from being pickaxed. only way to get closer is to place a draw bridge that then opens towards the tower. but you still need to remove enough keys from the perimeter walls in order to get close enough to the tower.
this kind of building is not a true unraidable system, it just works because it takes to much time to find all the keys and drill out every steel block before getting to one that its simply not worth it. in my team case, due to server settings, raiding our bases would have taken a single person 24 or more hours, making it so that before we would get raided we had time to sleep, go to work and come back home and seal every breach before anyone could have got into our main loot room.
this wont scale up with more players really, because TFP decided not to fix the issue that came with the new blocks health system (roland made a huge post about this back then asking about that), where if two or more players hit the same block it wont get damaged or it regens hp due to latency. this can be worked around by timeing your swings with pickaxes in a perfect way up to 3 players on the same block. it is impossible with augers tho.
another way you could raid towers is to ignore the perimeter wall by just jumping over it if possible or opening a breach through it and then starting to drill up from the bottom of the tower. this is by far the worst possible way due to the time it required to drill out blocks so that you can ladder up. there are more than 150 blocks vertically, and laddering up this way its just an insane ammount of time.
as far i am concerned, this is the only true way multiple LCBs can be abused and after 4000 hours of pvping and raiding thats the only way to use them that stopped raiders from raiding us, and us from raiding other towers.
Building larger villages with many bases or bases that can be jumped on top of are much much easier to enter no matter what.
cons
if due to the compensation in protected area a signle LCB would go larger than 15x15 towers would be even stronger. a draw bridge is what 5 blocks in lenght? it wont add much reach to the tower and if the claim gets too big that just means that no perimeter wall is needed and the only possible way to raid a tower is from the bottom up. As i stated before, this is so ineficient it can take more than 24 hours to do, effectively being unraidable if the owner of the base logs in and repairs everything before you get his key.
we wont be albe to build villages or multiple bases. thats also connected to the fact that we cant have multiple spawn points. as it is for now if you place bed 1 and then you place bed 2, you can only spawn in bed 2 untill it gets removed and then u start spawning back to bed 1 again. i am not sure this ever worked as intended btw.
LCB have a deadzone where enemies cant place another key in your area, but friends can. if the key gets deactivated by the claimed area and not the deadzone that just means larger clans like mine can still claim bigger areas, just having non overlapping keys will do the trick. even worse if the claim zone of one key just dont have to incase the other key, which is the system we used so far for efficiency (at least at the beginning, then we had keys on all blocks over time). this just means towers will still exist but single players who have a couple of small bases or just want to add more protection to a single small base will be in serious disadvantage compared to a clan tower.
i know i have been speaking about towers only basically. but thats the origin of the LCB issue as far as pvp is oncerned. having multiple keys allowed alot of ppl to build great villages and strictires just for the sake of beauty and with only one key it wont be possible anymore.
at this point i belive a system like in Rust would be much better, where your claim zone scalse with your block, and to counter the fact that this way you could claim the entire map there is an upkeep cost that scales with it, giving serious limitations to what you can do before the upkeep becomes unmanageable.
i different solution to all of this (and admitedly what i was hoping for) is the change to the vertical claim capability of the LCB. so that if a key rainge is 15x15, it would be so also vertically, effectively protecting a cubic area instead of a pillar from bedrock to sky limit. yes multiple keys will allow the same tower system and probably wont change much, but as everyone who played pvp in a serious manner and in a proper servre should know by now, LCB default cost is way too cheap and so admins ansays change it to a very expensive crafting cost to make it impossible or really time consuming to grind enough materials to craft way too many LCBs. OFC overtime that will be achieved anyway, but is a far better solution to only 1 key in my opinion.
as a last thing i dont think LCB area is really a problem, the real problem is the one previously mentioned where 2 or more players can auger the same block so to speed up the raiding proces. Time being the only factor that really matter in raiding matter this is a big issue. fix the issue so that many players at once can hit the same blick without having its health restored due to lag in damage syncing and tower wont be as safe anymore. I dont think there is need to remind anyone that a clan made of 5 players should and will always and anyway have an advantage over a single player, but at the same time a single player, who may not have time or resources enough to raid a big clan base, at least should be able to stand a change in protecting his own base. this means that as for a clan you have a big base will al the loots, for a simgle player is best to have multiple bases and the loots spreaded in all of them so not to lose everything at once.
ah. BTW... maybe fixing the issue where LCB strengh modifier between offline and online wont change if a player comes online, effectively having always OFFLINE strenght protection also would be great. so that admins can set high LCB strenght so that when someone is offline his base is really hard to get, but online, with a way lower LCB strengh is much easier so to encourage online raiding and giving a chance to the base owner to defend his base. this is a feature that never worked but is always been there. it will cause many new problems (like the owner of the key going offline during a raid so that the rest of the clan can defend with a much higher LCB strengh modifier on their side) but i would at least see that fixed and get a chance to test such a feature that never worked but had really good potential. is not perfect but with a bit of work can solve much more than a single LCB.
thanks for your time reading this baddly written wall of text.
EDIT: maybe a limited ammount of placeable LCB? like 5 max or so? with settings for admins to decide? yes? pleeeease? them being all active ofc.