Getting rid of PMI advice/strategy

Looking for some advice here. I am not sure if this is a good way to look at this, but I keep thinking about it, so I thought I would get some input. I bought a house a couple years ago with a minimal downpayment. My rate is 3.75%, so rather than make extra payments, I have been putting my money elsewhere (retirement accounts/brokerage account). However, I am paying $86/month for PMI which comes out to $1032/year.

I currently owe around $19k until I reach the 20% equity threshold to get rid of PMI.

Now, here is what I have been thinking about. Let's assume I have $19k sitting in a brokerage account which has been earning an average 8% ROI. That would equate to $1520 earnings over the course of a year. My thought process is that since the $1520 is more than the $1032 I am paying in PMI each year, I should keep my money where it is and not make any extra payments on the house.

However, as the months go by, the principal I owe to reach 20% equity will dwindle to a breaking point number where an 8% ROI will be less than the $1032 I pay each year in PMI. This breaking point number is just under $13k. At this point, it will make financial sense to make a $13k lump sum payment toward the principal balance I owe on my house, and thereby get rid of PMI. At least, this is what I have been thinking.

Thoughts on this strategy? I am sure there are other factors I am overlooking.. Any advice is appreciated.