The value in "complex" carbs over "simple" is the fibre and micronutrients that comes along for the ride. They're mostly still present in the treated oat milk (a lot of the insoluble fibre will be discarded, but the soluble fibre responsible for the beneficial health claims of oats is kept).

Starch vs. the maltose that the treatment produces shouldn't make a material difference in most peoples diets. It's all glucose in the end. (Maltose by itself has a higher glycemic index, but with the fat, fibre and protein it won't matter.)

Yes I understand the difference between complex and simple carbs. Even if it doesn't matter very much I'd still rather avoid simple sugars.

For example, I'd rather buy Elmhurst Oat Milk (https://elmhurst1925.com/collections/plant-milks/products/un...) that uses a different process. It has fewer calories and zero added sugar.

If I wasn't trying to avoid simple sugars I might have never found out about Elmhurst so to me it is worth it just to find better products.