This term "locked drag" gets bandied around very loosely Jim.
First, as you will know being an experienced angler there is really no such thing (unless your reel is broken). Even if you tightened the drag knob with a wrench, the drag is still not locked, it is just ridiculously heavy.
Southern Oman is not so different to other global locations which hold large GTs, although there are number of spots where the really big fish do sometimes hang in very shallow water. In those spots, fishing heavy drag is wise if you and your equipment can handle it. If the GT is allowed to run far, the strong likelihood is you will hit some structure. In other spots the water is deeper and you can fish what might be regarded as "normal" GT drag of 10-13 kgs. In the shallow water areas there might sometimes be no choice other than the boat pulling the fish into deeper water with you at the back of the boat hanging on as best you can.
I would suggest it is really up to you as an angler how you wish to approach this. Personally I would fish a mix of heavy drag where it is absolutely required, and use a more normal technique in the deeper water spots. Rod selection is obviously a very important factor.
As always, those are of course just my personal opinions, and others may think very differently.
Good luck, and if this is your first GT fishing experience you are in for some serious fun, as well as shock as to just how powerful the fish are compared to those you are used to
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