Quarantine achieves absolutely nothing. All it does is hide people away, no one gets immune. 3 months later, people walk out of their doors and start getting it. End result is the same, apart from you took 6 months to do it, instead of 3.
What was the point of that ?
There are different levels to implement, depending on how much capacity you have in hospitals. If you are heading to be being overrun, you clamp down more towards quarantine. If you have lots of spare capacity, you slacken it off.
The point is the ONLY solution (assuming a vaccine is a long way off), is to get people immune and you need a certain amount to get there. How you want to do it, is the only real choice. Do it faster or slower.
The UK imo has it right. It's focusing on protecting the old folk, getting them to avoid contact, and let the rest process it and get more immune, impose stricter policies if it starts getting too fast, so they are less likely to get it later, so later the vulnerable are less likely to get it.