Black and white opinions are fine on the internet but they don't work very well in real life. You have to have nuance and make educated choices.
If the the small business doesn't use AI, they sure as hell still are using Intuit for bookkeeping or Sysco for supplies or Microsoft for email. You can't get any from indirectly supporting the mega corps. But you can minimize your impact by making smart choices, like picking the lesser evil sometimes.