Here is a discharge test of alkaline C cells, courtesy of our friend HKJ.
https://lygte-info.dk/review/batteries2012/Panasonic Pro Power C UK.html
At a steady 2 amps, they will be depleted in a little more than an hour.
Of course, as the voltage drops, the out put will drop, and the amperage draw will also drop, so on alkalines, it may run for a couple of hours, with diminishing output.
On low... one might get 6 hours of diminishing output. I don't really know.
Yeah, that strobe is a slight annoyance, but one quickly learns to double click past it to off.
Yeah alkalines suck bad under heavy loads; at 2 Amps you will get more runtime from AA Eneloop Pros AND you will get a higher Voltage under load for more consistent output. This along with leaks is why I almost never use alkaline C cells.
Running standard AA Eneloops, I got about 2 hrs runtime on high and over 12 hrs. on low with the Defiant 3C. I am not sure if it has a step down or not, but I am thinking that it probably does.