Mattison had plenty of positives with his profile, zero glaring weaknesses. Also the price was key - late 2nd in plenty of rookie drafts a la James Conner. Getting a quality Day 2 RB profile that late is pretty rare. While not as good of profiles, it is notable Darrynton Evans and Lynn Bowden are both easily in Round 3 of most drafts this year.
I get what you are saying about the difference of a single pick or handful of picks between round breaks in draft position. It's a blurry line for sure. My model is a progressive curve based on historical data, so while I have plenty of charts and data regarding the firm round lines as the threshold, my main probability metric/driver is a curve, so 32 overall and 33 overall are really close together as opposed to 'this RB is RD1 and the other is RD2' as if they were No.1 overall and No.64 overall in the most extreme example the other way.
The biggest combination of factors I am 'down' on CEH (which is a comment on being bullish or bearish based on the price point to get him) is based on his profile and, more importantly, the cost. If CEH was in last year's class and folks wanted to take him 1.01 over Josh Jacobs, no problem there. This year, it cost(s) 1.01, but among a much stronger collection of RB prospects, especially Jonathan Taylor. If CEH cost 1.05, absolutely, sign me up. But now it's 1.01+ with an even further rise off the Damien Williams news. I am out at that cost as I was before. I am much less reactive to pure situation than the average dynasty GM/ranker/etc. I absolutely miss to varying degrees on players because of this, but prescribe to the mantra of talent over situation as situation changes more than talent in NFL and talent, even if blocked initially, will eventually emerge and find a way.