The immovable of it gets exploited by pure tanks in PVP. There could be someone that uses it and is constantly activating it so they are always immovable, and even a pure tank to where they can't even be killed. The anti-tank sets out there, are of no use. Given one, can be cleansed. and they aren't blocking all the time to use that one other set for it to even be beneficial. Can sit on rocks and then they could just knock the person off with fighters skill crossbow ability making them fall off the rocks and have to climb back up all over again.
They are always immovable an always puts out the flame on their siege weapon an fires again. This is even done during a time when hardly anyone is even on making it hard to even 'zerg' them down. If you try to counter siege, they'll just move elsewhere an continue it or burn your stuff an continue sieging.
I just suggest remove that 'immovability' status from the skill so pure tanks don't just take advantage of it.