I am gonna throw in here a few thoughts:
Lets see how the SAID principle (Specific Adaptation to Imposed Demands) and that kind of "combine workouts" help you as a long driver more than just "normal" gym work.
What are the muscle firing patterns and biomechanics in each exercise that create the so called "kinetic chain" that is a must for any smooth power production, basically the same thing as "effortless power" what Jason Zuback talks about.
Endurance training helps you with what - walking to the tee box? Long days of hitting at Worlds? Helps you recover from hard hitting/gym workouts? Maybe, but not very important if you wanna get fast which is the same thing nowdays as having a chance at Worlds.
Boxing the same thing - you get very tired and build lactic acid in your muscles. That normally makes you only slower + how often do you hit tired in competitions? So where is the transfer to your sport - long driving?
Rowing...I very seldom row when I stand on the tee box. Neither do I run or ride the bike.
So back to the SAID principle: do that you wanna get better at, simple as that.
Didn't mean to put you down the Viking just saying that when you do exercises at the gym try to think a bit HOW and WHY those exercises affect your performance. Every exercise you do makes you better or worse because it affects you swing one way or another. Time spent in the gym has to be optimized because you have only X amount of time in the gym and it has to be spent wisely. X amount because you must have quality in what you do and not quantity which means you can't spent too much time at the gym.
You should do as "sport specific" exercises as possible is normally what trainers teach. There is little problem tough - it is almost impossible to do long driving specific exercises in the weight room. Sure, there are many fancy and complicated looking exercises that make the trainer look good because he makes his clients do them but after a little biomechanical analysis, analyzing the anatomy of the exercise and the muscles actions involved you realize that the exercises are worthless waste of time and often even have a high risk for injury. Doing for example different core rotation exercises have a high injury risk unless you can really control your hips, have strong inner core and good posture.
It's a real jungle when it comes to training and there are many different programs and methods that give great results. One thing is for sure though - you gotta find yours and stick to it.
It's like my former physical trainer from Finland said "the difference between the champions and the number two's is that the champs do the little things better than others". He is the expert commentator in Finnish TV during Olympic games and the best decathlonists coach in Finland.
Like I said just a few thoughts, didn't mean to be preaching
