Hi Sneha,
I believe that you're answering the question yourself, but there is a little missunderstanding there.
On one hand, remember that you're analyzing the domain authority, so what counts there are the backlinks and the magic that Moz takes into the mix. For mor information about domain authority, check this article.
On the other hand, blogspot is a HUGE domain, and has millons of backlinks, so it's completely normal for it to be really authoritative in the eyes of Moz metrics. And, the personal domain will probably always have less backlinks and have lower metrics.
Regading the harm in using, there is no harm. Also, you must take into consideration that there is almost none room for SEO optimizations when using a free blog host.
Hope I've helped.
Best luck.
GR.