Bwana Surya ,
It goes with the territory , tuna fishing occurs mostly in deep water and there is no reef to cut your line off such as in GT territories so no need for too high an initial drag required to stop the hooked tuna , too high an initial drag will tear off the jaw of the tuna anyway . Longer line in the spool is desirable , for me 300m is a minimum for tuna while for GT I am comfortable with slightly less than 200m .
PE8 is a erelatively thick line to cast with light lures ( 40~80 gr.)some 80m+ distance is required to reach to tuna school without spooking them hence , at least in Pelabuhan Ratu we use PE4 to PE6 for tuna popping but I believe if one were to encounter " cow tuna " over 100 kg , may be a heavier line is required and a long GT rod such as LR88 is desirable , most cow tuna school will spook much easier albeit they will take heavier lures .
When fighting stubborn tuna , it's more akin to marathon than sprint in the case of GT so a forgiving rod is better for the angler to withstand the long fight as there is no way to manhandle the tuna in deepwater .
Jon .