This might be a case of the AUS guys forgetting what it's like to have to build programs in Ontario! We shouldn't assume that a DIII NCAA transfer won't make an impact - there are a tonne of talented kids that forego major junior for the NCAA, only to get passed over by bigger programs. Then, once they get down to the states, their D3 "full ride" isn't as full as they think.
One example, by the way: now-NHL Linesman Andrew Smith was a high-end Jr B player who went the SUNY route for a year. When he came back north and joined Waterloo, he scored 21 goals in 42 career games.
I'm not an AUS guy - I've been involved in building multiple OUA rosters, including rosters that competed at the UCup.
What you say about Jr A/B players going DIII has some merit, and there are a very select few who return to USports. But, with all due respect to Andrew Smith - who did not win a single OUA playoff game in his 2 years at Waterloo - they are not the types of players who move the needle at the UCup. I would challenge you to find a single player who fit that bill and even played in the UCup.
Many UCup contenders have a smattering of veteran ex Jr A players in depth roles (ex-SJHLer Evan Vossen scored the UCup OT winning goal for McGill). I know that many good players come from Jr A/B, but my point was that it's odd for Ryerson to bring in those types of players as the 26th and 27th guys on a roster hosting the UCup. Better players exist, and you don't need to be Mensa to attend TMU.
There are always exceptions to rules. NHLer Mathieu Darche was a walk-on at McGill, NHLer Bracken Kearns walked on at UCalgary ... but each of those guys scored zero goals in their first USports campaign.
Point being, NCAA DIII is one tier below USports, and two tiers below the UCup. We could all be grossly underestimating these players, but I'd willingly bet that neither even plays in the UCup.