Rust's usage is a good example actually of when Sullivan actually did try playing youth in the top 6 - He would put Guentzel, Rust, and Sheary in top 6 minutes for stretches and didn't seem all that bothered with trying them there for more than a few games, but the last 7 seasons he completely abandoned that, which means the first 2 seasons were more of an anomaly while the last 7 are more of his standard with using young players. Rust was used a lot in the top 9 in his 2nd season, his first he put up all of 11pts in 41 games mostly as a bottom 6 winger, but in his 2nd year his speed was something Sullivan wanted to utilize with Crosby and Malkin and routinely had him swapping in to both their lines while also spending time on the 3rd line with Bones and Rowney. But majority of Sheary and Rust's time that year was with Sid.
For Rust, in his first 20 games in his 2nd season being used more in the top 6, he had 6pts, 3 goals. His ice time didn't decrease as much as Puustinen's. Puustinen had 8pts in his first 20 games and his minutes were drastically cut for stretches then demoted to the 3rd line immediately, for long f***ing stretches (9 of those games) he barely got more than 9mins (a lot of under 8mins and some even down to 5mins).
Rust in his 41 game rookie season, was averaging basically 12mins evenstrength per game, he wasn't even used that often on the PK, he barely averaged 20 seconds on the PK per game. Puustinen was averaging 10:19 EV/G while putting up better ppg. Drew was playing on average 9:14 EV/G in his rookie year, but his production was downright awful. Sullivan essentially wasted all of Puustinen's 2022-23 season by not calling him up once when Nylander got 9 games - Sullivan barely gave much opportunity to Gruden, Poulin, and Hallander that year and this was a season where Kapanen was completely lost as a player, Heinen was barely considered a regular NHL'er, they brought back some of Sullivan's faves in Bonino via trade and Archibald during the off season (another waste).
So anyone that thinks young players on this team will get a fair shot, probably not unless they miraculously produce in some really awful usage and he's forced to try them in the top 6 and even then, he might not give them as much rope as he did in his first 2 seasons. During a time when he should be trying more, he's trying far less and being insanely stubborn and has for years now.
That 2016-17 version of Sullivan, after winning a cup, was still open to even trying something as whacky as Wilson, Crosby, Hornqvist (in Sid's first game back after injury no less, lol).
Rust from his 2015-16 season to even his 2017-18 season was given a lot of opportunities and it took him another season or 2 with that kind of usage in the top 9 to finally break out and score 27 goals in his 5th season (2019-20). But the many chances he had in the top 6 in that span, Sullivan by then had Rust as one of "his guys" and so he would get a ton of opportunities while still being fairly streaky. He's probably the last player Sullivan would try like that until O'Connor this past season.