What you're not considering is that it's possible both for a situation to be enduring and critical.

In a pandemic, lockdown, or quarantine, really is the only effective tool of control without immunity-bosting therapy (vaccination), or possibly, effective treatment (antiviral therapy). Not having people get sick in the first place is your best option, and, due to exponential growth, the faster you respond to outbreaks or rising Rt, the better.

Add to this delays in disease surveillance --- by the time you start seeing cases and they are reported, you're already 1-2 weeks behing the curve, and for COVID-19 that means two orders of magnitude more spread than you've detected, there simply is not time to convene a legislature, undergo debate, deflect disinformation, misinformation, and faulty models, to legislatively reimpose tighter movement controls.

We're seeing this in China, Taiwan, New Zealand, Australia, South Korea, Italy, Germany, Spain, and in numerous other countries and US states as the pandemic is brought under control, controls loosened, rates start rising, and controls are reimposed immediately as the resurgence is apparent. And by doing so, several of these countries (Taiwan, NZ, AU, South Korea) have avoided mass outbreaks, others have limited those to specific locations (China) or brought generalised outbreaks under control (Italy, Spain, Germany). Ongoing vigilance and vigorous response remain necessary, shown by experience.

By direct analogy, an ongoing siege remains an emergency though it continues for months or years. Ask the citizens of Leningrad. And this virus is a siege, it remains outside the gates.

An executive acts, a legislation deliberates.

Both are parts of the government. Systems vary, but in most democratic states, both are ether directly (presidential model) or indirectly (prime minister) the peoples' representatives. The power is not absolute, and legislators act as a check on the executive, increasing or decreasing powers, perhaps removing from office if fully incompetent or abusive.

Again:

- Previous pandemics have lasted years, decades, and centuries. Your imposed timeframe is utterly divorced from reality.

- The principle mechanism for pandemic control is vector and transmission reduction. Reduce numbers and rates of contacts, likelihood of exposure, amount of contagious agent shared, viability of that agent: Stay home, wash your hands, wear masks. It's not high-tech or sexy. It is effective.

- Rapid and effective executive decisionmaking is required for response, there is no time for parliamentary delay.

- In democratic states the executive remains a representative of the people.

- Powers granted are neither absolute nor without check.

- Such governance and response is proved effective in numerous regions.

- Emergence refers not merely to the initial appearance of the threat but to the situation as a whole. If it has rapidly-emergent characteristics and properties, it is an emergency.
"A condition of urgent need for action or assistance: a state of emergency." (https://www.thefreedictionary.com/emergency)
But the case that all issues must be resolved in a single prime-time commercial broadcast segment, or a few scant months, is parlous poor made here.

And for the record, I've made similar arguments since the beginning of this crisis:

Six months ago: https://news.ycombinator.com/item?id=22273830

Five months ago: https://news.ycombinator.com/item?id=22528060