More treaty construction does not guarantee a larger Yamato

Would a looser treaty make Japan build an even larger Yamato?

Not necessarily. Tosa completions and larger carriers could reduce the pressure for an extreme design, while yard capacity would still limit size.

Completing Tosa-class battleships and building large carriers could reduce Japan's pressure to pursue an extreme later battleship design. Its shipbuilding infrastructure would still constrain the size of any new ship. Yamato is treated as already near that limit, with its expense crowding out other cruiser and carrier work. A looser treaty therefore permits several possible responses rather than a predictable increase in Yamato's size.