Long Course Racing- What does it take
Long racing over 70.3 is a grind. It's not flashy or fast as much as it is about who physically breaks down the least. For example, Chrissy Wellington used to be relatively "slow" at short fast stuff. So much so Brett told her NO when her goal was to try to make the Olympic Team. She just didn't have that speed. However, she was the absolute BEST EVER in the world at just not breaking down. Her "all day pace" was just far stronger than others. She never broke down.
Another example even more extreme was Hillary Biscay with Ultraman. She could not run much faster at 70.3 or shorter, but she could run a double marathon straight down the Queen K in Hawaii at 8:00min pace. She would just set it in diesel engine mode and never fade, no matter what.
On the flip side, I've seen athletes as good as medalists at the Olympics just not be able to endure the longer stuff and Ironman AT ALL. They are speedy greyhounds, but when it came to the long endurance events, their overall endurance and strength just broke down. Some of the very best ITU racers never go long because they just don't have that kind of durability and strength.
Can it be trained? Yes, in most cases it can, absolutely! In some rare cases it never fully develops due to limiters that don't allow them to successfully get the work required.
How many hours will it require for someone's endurance and durability to get to where they can handle the long races? That is highly individual, and what they can handle to get there may or may not ever happen. It also highly depends on the athletes goals and level they are aiming to compete at.
For most of the very top athletes racing in long course, they are handling 20-27hrs/ week consistently all year, maybe some more talented ones around 15hrs, but for the majority it's going to be up around 20+hrs. That means they have the time for that in their life, physically they can handle that without injury or illness, and they recover enough to keep backing that up. Some professionals are handling 30-35+hrs/ week to reach their goals. I know Meredith Kessler was training 30hrs/ week while she was pregnant. It's no accident that post pregnancy she came out and killed all those races.
Things like how much time in a person's life do they have, can they physically and mentally handle it, and do they like training that much. All these things come into play. It's one thing to say , yep... throw 30hrs a week training at me. It's another to be able to do that for months on end.
Is there a happy medium? Yes, there is. Could you reach your long course goals? Yes, I think so. You have to find the right amount for you and keep your goals in line with what you can handle.