but certainly not enough worse to require 55 CM runs prior to AK in the first place.
51 runs of WP (or CM, or PR, or AK) will get all DL. I don't know why people keep repeating 55 runs. It's 5010 tomes. 900 more for relic, but you can get it later.

Full DL with i55 weapon is not super-overgeared. Relic+1 and full DL with some AF2/Allagan or melded i70 crafted is overgeared.
Full DL will increase your survivability over full AF with holes in accessories (there isn't i55 rings for casters either in GC Flames or goldsmith), but its the weapons that makes it speedier.

I'll be in full DL before running AK because I like to be the one that can carry, rather than the carried one. And I have issues with Wall and its movement, giving me a margin of error is going to make others, who end up not wiping as much, not be angry. Not because its a necessity or can't be done otherwise.

I wiped 10 times on wall, but I could have tried until time up, then queue again, right there in that AF gear with a lv 37 GC bracelet and lv 34 belt, and eventually done it anyways. But when its me causing the wipes, I rather reduce the chances first.