I agree with the advice that you've received. If I were reading your application, my main concern would be that the situation would repeat itself where your grades will be going up and down.
So I feel your main task is to help me understand why that will not happen again.
I don't really think it's such a big deal from the perspective of your statistics, yes GPA matters but if you have a good GMAT that will satisfy any concerns about your ability to get the work done. On that note your primary focus should be on getting an outstanding GMAT that is above the average for those part-time programs. I'd say a 700 would be what you'll be shooting for.
So, as mentioned, the only other concern would be stability. So I would use the optional essay to elaborate why the conditions that led to your academic ups and downs no longer apply and how you might handle them differently.
I think what concerns me is not so much the freshmen year but the senior year. So it would be important to know more about why that happened. I'm kind of confused because you said things were going great and then you became hopeless or something.
I wrote a Blog on this topic,
https://mbaessaycoaching.com/2019/06/22 ... ow-grades/Posted from my mobile device