To "overpower the taste" means to have a flavor that is so strong or intense that it dominates and strongly affects the taste of something, making it difficult to taste or appreciate other flavors. Full definition
I don't use bananas a lot in smoothies since I feel like they're used way too often in most smoothie recipes, but they do go perfectly in this smoothie and don't overpower the taste of the rest of the ingredients. (heathermcclees.com)