If that happens you're right security budget will be fine. But the argument is there is no guarantee the price will keep going up at that rate. We already see it's slowing down. Consider the subsidy will eventually go away so transactions happening on-chain will be crucial to generate fees for miner...

As long as price (in fiat) compensates for halvings security budget (theoretically) goes up. Through state regulation or market forces there can still be a concentration of mining power that actually could result in a lower security budget (easier to attack) despite rising hash rate. Capture comes...