Oveagers like Mac Hollowell that end up back in junior should be viewed almost as students missing a grade in school and having to be held back, not good enough to advance to the next level.
The CHL even put limits on this to allow only 3 max overagers on a CHL team as the league is designed for younger development players mainly 17-19 year olds with more promising future potential NHLers.
Most OA CHL players are generally previously undrafted ones or late round 5-7 NHL picks and longshots, having been passed through 2 drafts already and with no place yet to move forward, stay on as vets as this might be the furthest they go in hockey.
But since they're undrafted they're seen as the bottom end of 20 year olds talent wise as the good ones move on from junior to turn pro. So despite the age and experience advantage over younger kids the talent level is not as large to hinder the development of the younger more promising ones.
If you look at the OHL scoring by Dmen, you will find Mac Hollowell leading the pack with 58 points on a strong Soo team. #2 Ryan Merkley (age 18 & SJ (2018) Round: 1 (#21)) with 55 points and #3 Bode Wilde (turned 19 last week& NYI (2018) Round: 2 (#41) with 51 points.. Now if the Leafs had Merkley or Wilde those would be considered developing prospects to be more excited about.
Heck 5th in OHL dmen scoring is Nicolas Mattinen (age 20) drafted TOR (2016) Round: 6 (#179), a player the Leafs let walk unsigned, he went through the 2018 draft undrafted and now a UFA and has 16 goals and 48 points. Like Mattinen, Hollowell should have been drafted in 2016 when first eligible but likely considered too small 5-9 back then and in 2017 entry drafts until Leafs took a chance and that only likely happened because of how close Dubas is to his former CHL team the Soo. If Dubas didn't take him he might have gone through his 3rd NHL draft and now be a UFA. IMO
Lets put this in perspective .. 5-10/170 lbs Dmen are not in high demand in the NHL no matter how many CHL points they put up as 20 year olds. Certainly not a Babcock type player based on his preferences s past history will tell us.