In your opinion. Remember Tamou, Zane, and Capewell were rookies too at one stage.
Let's also remember that they all debuted at an older age, and still had to pay their dues.
Debut ages:
Leniu: 18
Tamou: 20
Tetevano: 20
Capewell: 23
Number of games in debut and sophomore years:
Leniu: 5 games (Rnd 21 - 25), and 6 games (and counting)
Tamou: 12 games (Rnd 8 - 26 in and out of team), and 19 games (only 2 starting)
Tetevano: 5 games (Rnd 20 - 25) and 13 games
Capewell: 4 games (Rnd 18 - PF in and out of team), and 16 games (playing Wing, Centre, Second Row, Bench etc)
Let's also look at how the teams that these guys played for were tracking when they came into the NRL
Leniu: Panthers finished 10th and currently 1st
Tamou: Cowboys finished 12th and 15th
Tetavano: Knights finished 8th and 12th
Capewell: Sharks finished 3rd and 5th
So we've got 3 players who all took longer to debut than Spencer. They were all eased into first grade from the bench, and not playing every week. And with the exception of Capewell they were all playing in average to poor teams.
Spencer has the luxury of playing NRL from the age of 18, gets to learn from 2 premiership winning props, and is on track on be part of a real premiership threat this year.
Personally, I think he's doing pretty well for himself already.
You can state 'this is my opinion' until the cows come home - but until you start to articulate WHY you have that opinion, people will continue to question those opinions.