"I'm most likely looking at a flat bar hybrid/gravel bike in the $500-$1000 USD range. "

My advice would be to not overanalyze the purchase. If you want a hybrid type bike, avoid the front suspension models, as they add unnecessary weight. Look for a wider tire instead.

I'd be surprised to find that there are any advantages generally among the brands you've listed. Maybe a larger dealer network, should you have a problem after purchase? That can be discovered by googling that brand's retailers in your locale.

In terms of quality or features at that price, they'll all be equivalent. Bikesdirect.com has the Motobecane Mulekick Express COMP at the $800 point, delivered to your door. Aluminum frame and carbon fork, SRAM hydraulic disc brakes, SRAM Apex 1 x 11, 40C tubeless tires. Perfect for what you've described. Can you find a better deal anywhere else? I'd be surprised to find out.