If it’s not larger, it’d be tough to justify the massive price increase for using it.

Price is based on perceived value, not cost to produce. There is no international court of price justifications; if customers are willing to pay $X you can charge $X.

Opus 4.7 was smaller and people still paid 4.6 prices.

gpt-5.5 isn't larger than gpt-5.4 but costs double.