Going to challenge that...
Tohu Harris, Jordan McLean, Blake Green, Marika Koribete, Kevin Proctor, Scott Drinkwater, Curist Scott, Tino Fa'masouali are just recent players. How about Matt Orford, Steve Turner, Steve Bell, Greg Inglis from yesteryear?
Whilst yes - there are some players who do shine in their system. But others are doing just fine when they enter another.
It's down to the player. Look at Tohu @ the Warriors. Him and RTS constantly their best players. KP @ the GC, Drinkwater standing out in a garbage side further up north. Tino doing well for his new club. Crippler repped for Australia whilst with the Storm, but did so again after joining the Cows. Koribete a Wallaby... in effect, I agree with you... Fatson was never a standout at the Storm. Showed glimpses but was not consistent.
But there are players Bellamy has groomed who have gone elsewhere and flourished, or at least, maintained some level of consistency in their playing ability.