That's not true.
You have four legitimate options before you get to potentially throwing a 7 up in the lineout. If you can't get it done with them you have bigger problems. How many takes did McReight, Tizzano, Gamble and Reimer take this year in Super Rugby? Australia have never used our 7 as an extra 6. We use them for a skill specific set in the pack.
He is on the smaller side but at his age he's fine. Every chance he ends up high 90s low 100s in weight which is fine if he maintains speed in the middle. Hooper, McReight, Tizzano all 101kg. Even Van de Flier is only 103kg