The problem comes from this tendancy to only talk about one class at a time or one class vs another class. If you look at how sieges unfold, I don't know if you can even say they are AS overpowered as some other abilities, let alone more overpowered.
Phases/types of a siege include to my mind:
1) Trying to get through the gate (tower/outer). Defenders are trying to kill people with oil and people who run through LoS killing ground.
- As attackers, shroom don't do much here except make it hard for defenders to get in, and they don't even make it that much harder. Using a controlled shroom on the tower oilpot is worth doing, but now shrooms grow with ML9 conv, it's much easier for enemies to react to it, and there is an easy way to prevent it happening in the first place - shoot the the ani before he can place it, since he has to be in range and LoS to do so.
- As defenders, shrooms (if used right) can make it hard to get near the gate, but if the attackers either use zombie rezz, GTAoE or a CCer standing off shroom farming, it completely negates their value
2) Trying to get through inner gate. Defenders are trying to use both oil pots and battlement/window attacks to keep attackers off.
- Attacking, shrooms make it much harder for defenders to arrive, because they can set up hard-to-negate killing fields. If you can get a foothold, they can also make oilpots and roof no go areas for the defenders. I believe this is the main area of OP shrooms, though assist nukers always made it hard to get into a position for oil/roof shrooming and warlocks made it much, much harder.
- Defending, shrooms can make the courtyard a hostile environment for attackers, but again a simple zombie rezz, GTAoE or dedicated CCer hugely reduce their value.
3) Stair/lord's room. Attackers are trying to get to lord and kill him.
- As attacker, shrooms are hard to use here. LoS and GT issues make them easier to kill than cast. If you are lucky enough to get a foothold, they help maintaining it, but GTAoE and zombies generally clear shrooms at frequent intervals, making them a waste of power.
- As defender this used to be one of the strongest aspects of shrooming, but now is much less so. In towers, the zombies, siege and GTAoE make it hard to actually place the shrooms, due to interrupts and stacks die very quickly once placed. Even if you manage to maintain a shroom-based defense, the attackers now just knock the tower down and overwhelm you. Inside keeps on defense, shrooms are still very strong, though clearly not as strong as pre-zombie.
If you compare this to how other abilities affect siege, I think you'll find zombies are at least as powerful - any situation where people are forced to congregate in close quarters, a few zombies can have the effect of killing people, interrupting or making people run into the open where people on battles ments can kill them.
Warlocks are also very strong in the siege phases where people stand on walls. Anytime someone moves into the open, they are shot down at a speed that used to be the province of multiple assists, and multiple assists are rarely able to produce a coordinated reaction as quickly as a single warlock.
Even GTAoE, which is nothing new, is arguably more powerful than shrooms. With the low HPs shrooms now have they get killed quickly by GTAoE, and if you try to place them somewhere not being targeted, they are usually in a place where people can shoot them from the walls. Conversely, you can GTAoE large groups of people very easily, preventing them healing and keeping them interrupted.
That's not to say Anis are not very powerful in siege situations. They are certainly right up there at the top alongside other strong siege classes. But realistically, there are other classes with high impact on siege. If Hibernia dominates siege situations on some clusters it no doubt owes something to animists, but other factors (like Bainshees) play a large role. Also, there is the consideration that the strong siege abilities on other realms are in some cases on classes not played much. Animists are good for PvE, so a lot of people have them.
