the 2 guys who the leafs have let go that i remember not agreeing with at the time because they didn't have enough (any) time in pro were verhaeghe and dakota joshua. verhaeghe who was famously a contract slot dump before playing an AHL game for grabner and joshua who the leafs didn't sign and dealt his rights after college (could have been his decision to not sign with the leafs, not sure). but i liked both of them and was disappointed when they were dealt. joshua especially is disappointing cus he's kinda exactly what the leafs could use right now. but i also liked riley stotts and ryan mcgregor and they've both turned out to be nothing.
i watched a lot of the marlies back then and marchment and brazeau didn't look like they'd ever get close to nhl regulars. the fact that they have, imo, is more on them sticking with it and making it than the leafs giving up on them too early. i've never seen a point in dwelling on letting go of guys who didn't look like they'd make it at the time. and with someone like marchment, even if he wasn't traded, probably would have just been lost on waivers anyway, but brazeau showed almost nothing that was worth keeping around. that may have been covid affecting his development and in hindsight maybe they should have considered that before letting him go, but hindsight is obviously 20/20.
anyway all i'm trying to say is development isn't linear, sometimes guys break out like 6 years and 3 teams later. it happens, nobody can tell the future and there's no point dwelling on these sorts of things because more often than not nothing comes of the players who looked bad and were let go lol. the leafs just happened to be a cursed franchise.