The Incoherent Concept of 'Proportionality' under Article 21

I'm totally scratching my head here - what exactly is the court's take on proportionality in Article 21? I mean, on one hand, it's all about balancing individual rights with the greater good, but on the other, it's super vague. Take the Romila Thapar case, for instance - the court held that the restrictions placed on her by the Unlawful Activities Prevention Act (UAPA) were proportionate to the threat posed by her, but only because the government couldn't provide any concrete evidence of wrongdoing.

BUT, if I'm not mistaken, the Apex Court has also held in other cases that the state can't justify a restriction on fundamental rights by merely citing national security or public order as the ground. So, what's the benchmark for proportionality?