Optional essay to discuss why i left my last job?

I'm sort of in a dilemma regarding the optional essay and need some advice. So I left my last job early this year after being there for 5+ years. Although i liked the job in many ways, I am not happy with the direction the industry is taking and also felt totally drained from the stress of the job. After leaving i got a few full-time offers but did not want to go back into the same industry. Meanwhile, I have been working on several part-time projects since then, that i find quite interesting, but are unrelated to my previous job. One of my recs is from the previous supervisor and another is from a current supervisor on one of these projects.

Someone whose opinion i value told me that i should discuss this in the optional essay since he thinks my resume since leaving my last firm looks a bit "random," giving off the impression that i'm a dabbler and don't have a coherent theme or message. Although I see the merits of his argument, I'm very uncomfortable about using the optional essay to talk about this since it could easily come across as defensive. Also, plenty of people do quit their jobs to work on random stuff and still get into top b-schools. So I'm not sure if an optional essay is really necessary.

FYI, the same person i mentioned above me thinks my mba essays, especially the career goals/why mba essays, are extremely good. He is just a bit concerned that i might come across as someone who does not have a clear "theme" in his career, something i disagree with since i was at my previous firm for 5+ years.