A 2019 study says the sourdough bread digestion is faster when long-time fermented:
First, we showed a prolonged transit time for the baker’s yeast bread
and a faster passage of sourdough breads, especially when made with
traditional and long-time fermentation.
Unfortunately, only 3 fermentations have been studied:
Baker's yeast only dough: 2 hours of fermentation at 30°C
20% of sourdough (4 hours fermented) + 1.5% baker's yeast: 1.5 hours of fermentation at 30°C
20% of sourdough (24 hours fermented) and no baker's yeast: 4 hours of fermentation at 30°C
The sourdough was made with Saccharomyces Cerevisiae, like baker's yeast, and with 2 Lactobacilli (Lb. plantarum and Lb. rossiae).
Link to the study: Sourdough Fermented Breads are More Digestible than Those Started with Baker’s Yeast Alone: An In Vivo Challenge Dissecting Distinct Gastrointestinal Responses
About baker's yeast fermentation, my theory is that a longer fermentation with less baker's yeast lets more chances to sour bacteria and sour yeasts to devellop themselves. Because wheat flour is rich in lactobacilli (according to french wikipedia: lactobacille). So the long-time fermented dough with only baker's yeast, could have properties that may be closer to those of sourdough long-time fermented dough, and so, long-time baker's yeast fermented dough may also be more digestible.