Walker:
Think Walker is the tough one out of these 3 - had he been playing his best position at Centre and sucking, it would be easier to stick it to him and keep him in the Reggies.
Fullback is such a different position to manage than Centre or even 5/8th - defensively look at what Turbo has done to this backline, and look at Tom's movement and the way he reads the game, screams at his troops, and is always in the right place. That can't be learned overnight - and I think Walks discovered how hard it is to just shift into that position and get it right.
Des used him there he thinks Walker is a good instinctive footy player and would pick it up as he did 5/8th. Maybe he didn't want Harper to have a baptism by fire. Given Harper's performance though Hindsight may argue that Harper would have coped and possibly excelled, just as he is doing now. Harper is a super talent in retrospect.
Suli:
As it is Suli is the easiest to leave out. He simply needs better form - he's an underperforming Centre in Def especially, and is not adding enough starch in attack to overlook his poor Defensive decisions. He may not miss the tackles specifically, but his positioning and inability to read the play is dire based on what I have seen - it really worries me actually, as its like he has no footy instinct when defending at all.
Then again, if Suli lifted as much as the rest of the team with Tom's return it would be a frightening prospect for other teams.
Siro:
Siro is 2nd easiest to leave off - repeatedly making bad decisions in attack that starve our outside backs of any ball and in turn this eats at their confidence. The guy could be so much better, but either the way Des uses him, or his snap decision making in-game are just off a bit. The younger guys like Guac, Sipley, Schuster and Keppie just seem to want it more and are more cohesive team-players.
Siro does bring some experience, but that has been out-done by enthusiasm and energy in the modern game - Siro's experience is not in the new 6-again era and imo counts for less. The best team in the comp are the least experienced in terms of games played.