It might. Some teams take chances in the late rounds. London took Alex Formenton after the 10th round. Steve Mason and Patrick Maroon were both taken after the 10th round in 2004
Here's pick # 302 by Niagara in 2012
Blake Siebenaler - Elite Prospects
Peterborough - Round 12
Steven Lorentz - Elite Prospects
The question is more whether teams would change their strategy or not. Some use their late picks as flyers on NCAA bound players. Would they still take those flyers with earlier picks and sacrifice the guys that typically don't play in the league with 8th and 9th round picks? Dunno what that impact would actually be.
Also, there is the under-18 draft to also consider. If teams lessen their main draft and then more viable players become available in the under-18 draft, it may not impact anything at all.
We also need to consider the few players that are drafted to deep rosters and don't get a chance but may have gotten a chance in another organization..
The reality is it is very hard to predict exactly what would happen.
That said, if it is two or three players per year, does that have a league wide impact? And would those player syou referenced never get an opportunity to play in the OHL had they not been picked as 16 year olds? Possible but we do see walk on's make teams too. Hell, Claude Giroux slipped through the entire OHL Draft and signed in Gatineau as a walk on/invite.