It looks like an oddly lopsided low-tech ship, judging from the armor plates on the sides looking like those from the Onslaught. Wouldn't say it's an upscaled Falcon.
Coloration of the armor plate looks more midline to me, though it's a bit hard to say with the noise on the image. Still, the visible armament fits with low-tech.
That is absolutely a Prometheus with a bunch of armor bolted to the sides, the lumpy orange bow gives it away.
Plus it has the Prometheus round front and the same overall hull style.
I don't see the resemblance. There's a hard straight line on the left side of the "lumpy orange bow" that simply isn't there on the Prometheus, the Prometheus tank body is more of a red than an orange color, and, while it might just be the image quality, the orange bit doesn't seem to have features consistent with the Prometheus tank body.
I agree that the other one's definitely an Atlas conversion, though. Looks like maybe a Hephaestus, a pair of Heavy Autocannons, and a launch bay on it.