I think the reason for capping stratum is twofold. It can be messy, the same as for a dirt substrate. Also its expensive, so for larger tanks capping with a cheaper sand substrate is more cost effective.
However, stratum isnt intended to be capped, and sand will gradually work its way down through the stratum.
I often find when you get conflicting reports/reviews its because there is no definitive answer. What works for one person in a situation might not for another in a slightly different situation. You will have to find what works for you in yours.
I would also look at the type of plants you intend having. If you are going for low demand "easy" plants, then planted substrates arent really needed and you might be overcomplicating. Some plants dont need substrate at all. Those low demand plants will be fine in standard aquarium gravel or sand, and rooted plants can be supplemented with root tabs. If you like the look of the stratum, i wouldnt cover it. If you just want it for the nutrient benefits and prefer the look of gravel or sand, then cap it, or just go with sand/gravel and supplement rooted plants with root tabs.