Hi Phil this is a good question and one at present that there isn't a definitive answer for. There really aren't anywhere near enough intervention studies/research projects in climbing and mostly our conclusions in the industry are still being based on experience and intuition*. In terms of the models that we've used with climbers over the years, we've had much better results from using polarised endurance training, where we eliminate that middle ground that operates around the lactate threshold.

With reference to your question about whether the very high volumes of low intensity training are useful for you, then this really comes down to being objective about your own physical profile and how this matches up with your goals. Just because the science says that it's great to train high vol, low intensity doesn't necessarily means a single individual needs to do that if their localised aerobic performance is already above what's required on the route OR that there are other elements that are much more more important to work on!

* I'd like to say that after a number of years of working with a very broad range of climbers and handling thousands of pieces of data we've got a solid grasp of what is and isn't effective.

Quoting:

In pure endurance sports (e.g. running, cycling, rowing etc) the scientific consensus has settled around an 80/20 approach to training with 80% of work being easy (just below LT1) and 20% being hard (generally above LT2), even for athletes who are competing in events as short as 4 minutes (e.g. individual pursuit in track cycling), the theory being that low intensity and high intensity work build endurance through different pathways and you can do a huge amount of low intensity work and still recover pretty easily.

Ignoring anaerobic work for the moment the equivalent approach for maximising endurance (e.g. for long trad / sport routes) in climbing would be 80% ARC training and 20% aerobic capacity & aerobic power training (along with supplemental strength and conditioning work). Does this work for climbing or is there little point in doing large volumes of low intensity training like I do for running / cycling?