He's correct. Any good AIM can play Jett, Sick can, Shah can, TenZ is getting jett slot here but difference between them is not a big gap so he's just taking a "better slot; ez slot" while all other players needing to play at uncomfy role. with sinatra flex everyone could play at their best role without any issue. Nowdays at high rank anyone can play Jett well tbh.
I think SEN only got sucess because during first LAN tournament (Jett buffed not nerfed) was TOO STRONG. So TenZ with Jett could make a big difference but nowdays he can't, being flex is way more better now but he can't flex.