All of that can be true, and are major issues why I think Sullivan isn't a good coach and has firmly worn out his welcome here, while it's also true that blaming him for their horrible drafting and developing is downright silly.
Sullivan is why so many NHLers and prospects have come up to the NHL and have had zero impact, only to be cast away quickly. It's not Sullivan's fault that JR and Hextall drafted a bunch of shitty players that didn't even end up good AHL players. They don't have many young players right now because JR traded picks away like candy and Hextall didn't do anything to replenish the farm like he was brought into do.
In the draft history you posted (along with their 2015-2017 drafts), they didn't have 1st rounders in 6 of 8 drafts and only had 8 2nds and 4 3rds. With those picks, they traded a bunch of them (Addison, Hallander, Gustavsson, Clang, and Sprong) and missed out on a bunch of them (Lauzon, Phillips, Legare, Hall and arguably Bjorkqvist). What young players were even left for Sullivan to hurt? It was Poulin, Hallander (after he was reacquired) and Puustinen, that's really it.