In all cases of possible exploits or possible glitch playing on official servers, always report via the link in the official rules
Some very large bases are built by clans. If a clan has been on a server for a long time, even if clan member have move to other servers, all of the clan resources and materials remain. Aquilonian build pieces are the same as all other tier 3 build pieces. Black Ice build pieces are harder as they need Black Ice as well. Argossian, Turanian, and all the other DLC base pieces have the same ingredients and strength.
Funcom made changes to the Trebuchet. It now reaches Huge distances so you can likely reach that base no matter how high it is.
If you build with hundreds of build-pieces your own game starts lagging. At a certain level you would find the game very hard to play. If that player has built so big, then their game will be very slow. Most times, players that build so big will move to other servers or games because it gets boring. If the player moves to another server then the game Decay system will make their base, no matter how large, start to decay and disappear.
You can also check other servers that don’t have players like that or look at private servers that have Admins that stop exploits.
But use the link above to report the player’s base if you think it’s an exploit.