Yes it still might take 99 runs to get the mount unsynch but most of the time you can kill them much faster unsynch and on top of that I can farm those with my small group of ingame friends which does decrease the amount of mounts needed for the whole group and the time that you need to run it. At the same time the drop rate is often increased over time thus its goes faster this way too. So less people needed, faster clear time and higher drop rate. Thats quite some good arguments for me to run it unsynch later. I dont need the mounts right now (they are not that unique that I want them so much..I only farm them for the completion) so why should I throw myself against it synch?
Please dont forget that there is more to this game than fighting. I dont raid and I barely do any dungeons. (I find them boring) I mostly craft or try to complete achievements. I also like to collect pets and glamour. (Which is the main reason why I even run dungeons more than once) In the end just trying to get the yellow gear for all my crafters will take me a long time. Just because I dont like the fighting part of the game that much doesnt mean that there isnt enough other stuff to do. And crafting is also a perfect way to catch up to some videos while doing it. Maybe the second part of the Deep dungeon and Eureka will get my interest more (and Palace of the death is something that I ran for hours) but I will not waste my time trying to collect those copy paste mounts synch while I still have enough other stuff on my plate.
And you are right, if you take away the extreme fights and raids you will only have dungeons, 24 man, Palace and Diadem (which is death). Only one part of it was fun for me so thats probably also a problem of mine. Why should I run dungeons to get gear if I only use them for dungeons (and maybe an extreme fight) anyway? I really hope that Eureka gives us more interesting fighting content and not Diadem 3.0.
