Takes 6-7 months of playing to hope to be able to reach sennin rank in uk bracket, in other regions more. If you don't own at least 11000 initiative my suggestion is to wholly forget about arena, like the feature doesn't exist except for training.

Of course, 5 months ago 8600 was like now 12500, since the number of servers who had f2p people with higher initiative than that were pretty low, but now even server 400-450 have people with that level of initiative for free, while at the time you are talking about only servers before 200s had people with that level of initiative. Myself in 1st season had less than 7000, now i have over 13000 in merged server 291-306.

Try to remove pieces of equipment to reach 8600 now and go there. You won't even reach, very likely, kage rank, unless you own whale teams.