Is that all the science to it?
Gut training is consuming large amounts of carbohydrate (preferably in the same form you intend to use when racing), yes.
However, for many people eating so much of a very sweet food becomes very unpleasant.
It is very easy and cheap to make at home a gel by boiling in water corn starch mixed with fructose in a microwave oven, for a few minutes. Swallowing such a gel should feel much less sweet than the same amount of a sugar solution.
As far as I know, the only difference between such a gel made at home and the commercial gels for athletes is that in the latter the starch is pre-digested with some bacterial enzyme, so that the long starch molecules are broken into short molecules of dextrine and maltose.
This processing shortens the time until the absorption in the gut, but I am not sure if this is really an advantage in all cases. A slower absorption will maintain an elevated blood glucose level for a longer time after ingestion, which may be preferable if you feed periodically, because it avoids wide fluctuations in the glucose level, while a faster absorption might be useful for an immediate recovery when the glucose level has been severely depleted by not feeding for a long time.
It’s also about the methods of achieving that under stress without spewing it all back up. Ironman athletes would stuff their faces on the bike under the assumption that this volume of carb absorption wasn’t possible while running.
Some of the challenge in research will come from competitors not wanting to publish results to maintain an edge. It is mitigated by the visual of the race by (you can see athletes pounding carbs), as well as the nutrition companies wanting to sell more product. This will cause them to publish some information to convince us amateurs to quadruple our purchase volume ;-)