@J.D. I know its' getting stale but thought I would reach one last time on this topic

@matvdl Just trying to think what other advice I can give. You mentioned you've had other tables that were 80-90% fragmented, were those also mostly insert only tables? Did they have a clustered index on them?

In those cases when you did index maintenance on them and saw performance gains, that was more likely due to the statistics of those tables being updated, especially if they're at the same scale as this table you're referring to (billions of rows). Statistics maintenance is a way more important than index maintenance, especially for larger tables.