TurboTax is following the IRS instructions and procedures. It's fine the way it is. Thousands, maybe millions, of people do it this way every year. The IRS has a form, Form 8453, specifically for mailing attachments separately when you e-file. TurboTax will create Form 8453 for you and you attach your detailed statement to it. The IRS understands what's going on and will treat the statement as if it was attached to your tax return.
When you make summary entries on Form 8949, the IRS instructions say "Enter the name of the broker followed by the words 'see attached statement' in column (a)." TurboTax is following the IRS instructions. They are not going to change the wording that IRS says to use.
