Cut / open body sheet metal with Dremel or multitool instead of angle grinder?

I'm just wondering if a Dremel is powerful enough to cut/grind/sand body sheet metal (how thick is that on a 23-year-old European car?). Specifically, this is a one-time job involving drilling a 16cm diameter, or 16cm square, hole into the (ungalvanized) 23-year-old body (in a non-visible, dry area). My thought was, Flex is "too much",…