I disagree a little here. Three years and it's 'your' team. I don't necessarily think he could have landed a big fish, primarily because they probably wouldn't choose to sign at Manly...but history shows that clubs turn over rosters when they want to (looks at Ryles this year and Ciraldo in the last three). Seibs has chosen to stick with a lot of what he already had, believing that it's good enough to get the job done.
I get that people will argue that a number of players are under contract and cannot be moved, but we've seen time and time again what the tap on the shoulder does. Players get shopped all the time and Seibs has elected not to do this. I'm not even suggesting this is the wrong move from him, just pointing out that after three seasons, you've essentially got to own what you've got. Every coach arrives with a previous coach's leftovers and given a club must spend 95% of their cap, paired with the NRL no longer allowing heavily back-ended/deferred contracts, walk into essentially the same predicament.
What we have at Manly is a strategic move by Seibs to go all out for a premiership now, rather than rebuild like say Ryles is doing at Parramatta. Right or wrong? I don't know...but he's made a choice to stick with the core group and put some bargain forwards together, rather than tear the place up and start again. For this reason, after three years, it's partly on him whether he has the cattle or not.
Just my 2 cents worth.