There is always the difference between a better "OHL player" and the better "NHL Prospect". Rossi is a better OHL player at this time (although he is old for his draft year) than Monohan and Konecny by a fair bit. I think he is only slightly better an NHL prospect though, as both Monahan and Konecny had some NHL qualities to their game that Rossi is a short on. On the other end of the spectrum, Corey Locke was a better OHL player than any of the others in his draft year, but not close as a prospect given the speed and size issues. These don't haunt Rossi in the same way, but there is at least a bit of that risk to his career given his size and lack of elite skating. Now he is much thicker, stronger and a better skater than Locke, so I'm not inferring they are the same. But when evaluating the prospects as future NHLers, Monahan was a big skilled center it was clear would likely handle NHL physicality - some minor skating concerns as a prospect. Konecny was one of the best skaters in the draft with an incredible motor whose size and injury risk hurt his stock (and a bad team).
Now obviously Monahan and Konecny have both panned out well, and are more valuable than their draft position given the risk of players even in the 1st round. If Rossi turns out to be as good as either player, I think the NHL GM drafting him will be very happy.