Yeah, the star cannon will kill pretty much anything in seconds. Eater of worlds exclaims "OMGWTFBBQ" as he's blown into smithereens. Of course, you could achieve the same effect with a Sunfury while standing in a skytower (He'll tend to fly up towards you from the ground, through the tower, making it easy to smash multiple parts with the flail all at once for massive damage).
Even players in full molten armor with max HP get killed in two or three shots by the star cannon. Of course, you can also kill them in less than a second with a phoenix blaster, without having to farm for stars (it's semi-auto, but you can just click rapidly). It has an almost instant reload time, and meteor shot is even more deadly in buildings.
Personally, end-tier PvP isn't quite as interesting to me as PVP with either new characters or scenario games:
I'm interested in a kind of scenario world where different teams have different goals, all the players start new characters specifically for that world, and the game takes place until a win condition is met.
One possible scenario:
Two teams build a base, with NPC housing, and go to war to try to collect all the NPCs in their own base. Whichever team ends up with all the NPCs wins. They can pull whatever tricks they want to, such as building ebonstone towers, corrupting land, building dungeons to spawn monsters, making an orbital magma cannon to EX-TER-MIN-ATE the enemy, or running into the enemy base carrying water candles during a blood moon.
Another scenario:
Castle attack with one team constructing an evil castle, without NPCs, defended by monsters (both ebonstone and dungeon background), potentially manning safe tunnels with a different background inside the walls (to protect against being attacked by the monsters) while holding water candles to increase the max spawn amount, with the other team trying to breach the castle and reach the center, to destroy tables and capture water candles sitting on them, and take them back to their own base successfully. The entire water candle room would be done in hellstone ore or hellstone brick. How they breach the castle would be their choice. How the castle is designed and defended would be the choice of the defenders. In this case the attackers would have all the NPCs and the defenders would have none, but both would start with new characters, the goal would simply be to either kill all the attackers or breach the castle, get the candles, and destroy them by throwing them into lava. (It would be nice if it was possible to have the candle drop on death, but alas. You'd probably have to give it back to the other team or something if you get killed before you can escape and destroy it.)
The materials to construct the castle could be provided to the defenders so that they can build most of it rapidly (along with at least one obsidian skull), although estimating how much they need could be a bit of a trick. Both teams would probably want to try to find materials to make decent armor, weapons, and tools, before fighting each other, although if the castle isn't preconstructed there'd be some incentive for the attacking team to rush before it could be completed. (We'd probably have to rule that they couldn't attack until they had every NPC)
Rules would include:
1. No jungle or molten equipment or armor (Including both drops from monsters (Sunfury, flamelash, cobalt armor, etc) and craftables (such as the grass sword or ivy lash, phoenix blaster, etc)).
2. You can use hellstone ore for building purposes, but not for crafting.
3. Metal, Meteor, and demonite equipment and armor are permitted, along with necro armor, except for the star cannon. Yes, it uses meteorite, but it's right out.
4. Items found in the dungeon are allowed (Cobalt shield, blue moon, handgun, muramasa, for instance).
(There isn't a rule forbidding orbital magma cannons, but...)