You asked for advice and you received it from a cross section of premeds, med students and professional advisors. Yes, you could absolutely submit an app and wait for scores. Check MSAR. I'm pretty sure you will find just about every school will accept scores for tests taken through the end of September.
But that wasn't your original question. You asked whether you would be at a disadvantage. The obvious answer is that of course you will. You will be taking the test two weeks before the absolute deadline, and will be competing with people who have had completed applications in since the second week of July.
Is your primary ready to go? If not, do you have time to work on it while studying? What about secondaries? When were you planning on doing them? October? Are you wondering if that will put you at a disadvantge? (Spoiler alert: it will, since you will competing with people who had them in in July!)
Will it kill you? That entirely depends on how strong your application is. Will it disadvantage you? What did you think when you first posted? What do you think now? If you don't want to take another gap year, take your shot now. But realize that you not be on an even footing with the tens of thousands of people who will have submitted completed applications prior to 9/28, let alone the end of October, or whenever you think you could be complete.
From the AAMC website: "More than 35,000 students have successfully taken the exam this year, and we expect that 90% of AMCAS applications will have associated MCAT scores by mid-August." -- You will be in the other 10% from mid-August through mid-October.
