Should be noted that constipation relief is far from the only benefit that probiotics provide to your gut biome. Healthy gut biome has been linked to lower levels of depression and lots of other things seemingly unrelated.
You mean claimed to provide.
My guess is that for regular people the benefit is insignificant but it's greater for people with issues (dysbiosis).
And the type of dysbiosis you have will determine the effect of the probiotics. For some it can slow motility or cause constipation and others increase motility or cause diarrhea.
There's so many internal variables with your gut microbiome and there's a general lack of reliable methods to test your microbiome. This makes tests like these really difficult and also makes it difficult to treat digestion issues. Because of this, all gastro doctors can really do is slap on IBS/IBS label but not really have a course of action with any decent success rate.