The LVL 55 Grand Company weapon can actually be used for Ifrit HM and Garuda HM, even Haukke Manor and WP. My first run at Ifrit HM i had maybe only 1 piece of dl and it was no problem.
By the time you get to Titan you for sure want full DL, i was at ilvl63 and really had a hard time. I see that you are Archer, for the advise that someone said to get Primal weapons Ifrit>Garuda> Titan well maybe you may have luck
but after 40+ runs of Ifrit HM i have never seen the bow once and Garuda's bow is far better from what i have read. Our FC and LS ended up helping me acquire a crafting lvl 70 HQ bow in the end.
For dl gear itself i highly recommend to get anything that gives you more vit as it will be needed for Titan. CT others have said it better and i have yet to unlock it.