I don’t think it’s all that simple really. First off Chad Waterbury is a very knowledgeable guy, but remember there are literally hundreds of trainers and tens of thousands of body builders that are just as or nearly accomplished as he is, whom might give completely different advice. They might not be as well-known or published but they know how to get results. Each one will have their own take on how a person should be trained. There is no ONE absolute school of thought (i.e. total body vs. split routine).
TBT may be the greatest thing since sliced bread for most people but it’s not for everyone and certainly not all the time. Not too mention even Chad admitted that it cannot be done constantly all year, just like any program. I’ve been a professional trainer for several years, training and doing research for over 12, and from my personal experience with TBT its a great program! But, I have also added 30-40 pounds of USDA Choice to my frame (and frames of others) from doing the classic 1 part/day/week split. I think TBT does have the edge as it may work for a greater portion of the population, more often. But, the biggest keys to muscle growth are nutrition, stimulation, and variation. Therefore, I’m going to go out on a limb here and say that ALMOST ANY PROGRAM WILL BUILD MUSCLE! And, ALMOST ANY PROGRAM WILL PLATEAU!
Here is why: with the 1 part/day/week split, typically a trainee absolutely demolishes that body part, probably doing 20-30% too much volume. However, they also give that body part a full 7 days of recovery. If you broke this workload up over 3 days you now would have a total body training routine. (e.g. doing 15X8 once a week or 5X8 three times a week). Same volume, but different frequency. There is also something to be said about keeping the anaerobic system from being over-taxed. Some trainers feel that only stimulating a specific region of the body per workout allows the more efficient use it’s workout-limiting supply of oxygen and glycogen.
Having said that, I think training a body part at least twice a week would generally produce faster results. Generally, the recovery from an intense or heavy lifting bout is enhanced when that muscle group is worked again 48-72 hours later. The higher the frequency of stimulation the more nutrient rich blood floods the muscle and the more wastes are expelled.
So, I’m not a dinosaur that has been there and done that for 40 or 50 years, but in my experience and research, I have seen both total body training, the classic split, and many variations in between all put mass on folks. It’s mostly about variation and finding what works for you as there are accomplished trainers/trainees that have been training with the same parameters for decades!
I think your coworker could indeed benefit from the TBT program or any other variation from his normal routine. But, the new growth/strength he would likely experience would more likely be due to the drastic change in his training parameters. I’d bet if he did TBT for 6 months than reverted back to that split he would also see another growth surge.
Finally, being a woman and likely smaller than this guy he will have a hard time listening to you. That’s why 70% of my clients are women. Women are about 17,000% more open minded than men! And that is unfortunate because it sounds like he could learn a thing or two from you!