Kindly leave RPG elements out when arguing game mechanics. It does not help any discussion at all.
I'll try to get some clarifications from either GA CM or Support on what goes and what not, but my understanding (as being a German myself so i pretty much followed the stuff for the german servers as a player before) is that any way to *get* into the castle while the gates are up and have not yet been destroyed is an exploit, period. Not much to discuss about that, I think.
What's up next is my understanding of things and how they currently are, compiled from various sources of information. Take it as guidelines or as a point of discussion, I don't claim to make actual rules out of it because that is beyond me, but so far doing it like that worked good, and without pointless drama or cheating accusations.
That's that. To the other things:
Damage through line of sight issues in both directions, well, who casts the first stone? Towers are allowed to be built on the inside and outside of the castle, by both parties, and they clearly currently ignore LoS. A warden's pet is not the same as a player is in how the game works (its an NPC controlled by the player ... as for NPCs and line of sight...ask any random instance mob what it thinks about LoS

). There is not much that can be done about it atm except not using classes or buildings at all which is also rather a non-option. The owner of a warden pet has control to a certain degree but to my knowledge nothing and no one is forced to be a lame duck to be shot off due some arbitrary mechanic.
A really strict view could even say that even this is an exploit but then fighting at all is an exploit, this is rather something that needs to be changed by Runewaker. Also Suggestions like immunity to the permanent buildings while the gates are up (and once destroyed, BACK up and no enemy player is within ..as hiding after gate kill is also valid) may work, but that are game changes to be executed by Runewaker.
But, a strong advice from me would be:
Leave
permanent buildings alone, they don't attack or pull aggro.
There's no real excuse to attack them from the outside with
anything (No, "but RPG..." is not a valid argument, sorry)
Also while a warden pet can be set to engage on being attacked , or attack the owners target, the owner is still responsible for not abusing it on intent to kill off permanent buildings within the castle walls. If one claims to not even have that bit of control over the pet, well, learn it, and do it fast, or don't use the Pet.
TLDR: A fight is a fight, but the permanent buildings don't fight and are only valid targets when you are already IN the castle. Only legit way IN the castle is through a destroyed gate.
Honor guards and similiar stuff are to be covered later.