Is store-bought kimchi as good as homemade?
Only if it's unpasteurized and refrigerated -- some shelf-stable exported kimchi is pasteurized, which kills the live cultures behind its gut-microbiome benefit.
The short answer
For the gut-microbiome benefit specifically, what matters is whether the live cultures survive, not whether it was made at home. Kimchi was included in a Stanford fermented-food-diet trial's positive category-level results for increased microbial diversity, but some shelf-stable exported kimchi is pasteurized during processing, which kills the live bacterial cultures entirely. Refrigerated, unpasteurized kimchi -- whether store-bought or homemade -- is what the research actually applies to. Anyone immunocompromised should discuss unpasteurized live-culture foods with a doctor first.