I used to do a bit of casting from the rocks, but a long time ago.
I assume when you say 12kg is your sunset you are talking about the highest drag. If it is then you are braver than me
Unless I have some way to brace myself and have a good safety line I doubt I would be able to use 12kg of drag on the rocks, particularly with a reasonable spinning rod, and I tip the scales round 85kg.
I would use 10kg drag but on a fully rollered game stick & live baits. On the rocks its always a compromise between length of rod and useable drag. You can make a rod with a long butt but you may find they are awkward to use. The longer and stiffer the rod (& shorter the butt), the more lever the fish has on you.
To use 12kg of drag pesumably you would be using at leat 37kg line (or more) line and with that weight of line, with a fair bit out with a big fish on and an overun or other fault you will be in trouble trying to brake it off to prevent ending up in the water or losing your gear.
For me casting line of about 20kg is not out of the question and for this, for me the rule of thumb is 1/3 breaking strain fighting and 1/2 breaking strain when you are desperate. This means fighting with 6kg of drag which I would be able to manage with a reasonable length reasonably stiff rod. You can use a very fast taper rod which will make it easy to fight but will limit the lures you will be able to throw.
In this day and age with braided lines, diameter of line & flexibility being major limitations on casting distance no longer applies. You will be able to cast just about any size lure with the right rod & line combination but perhaps its worth considering whether you will be able to actually fight the fish in reasonable safety.
I would work back from what drag I can manage, decide on the line I wish to use, then the lure weight I can reasonable want / expect to throw and suit the rod to the lure. The rod just has to match the line/ lure weight.
You can always go for heavier gear and just run it with lighter drag, but a rod designed for the heavier work of high drags will seem a bit stiff when used with lighter drags.
I should add that the times I tried to throw poppers off the rocks I got very frustrated at how far I could get them compared to other type s of lures. Their very design makes them either big or light for their size (if that makes sense?) generally you need to cast lures a reasonable distance on the rocks whereas in a boat you just get the boat closer..