Furlough was not entirely necessary. No other country paid 80% of everyone's wages fgs. There were statutory benefits alright, but they were a fixed amount.
Yeah, it was necessary. As soon as the decision was taken to lock down, it became a requirement.
There are arguments to be had about amounts and eligibility, particularly later on when there isn't the excuse of having to cobble something together fast like there was in March 2020. But the principle of state support, there is no way of avoiding that once the state decides to prevent millions of people from earning a living.
The benefits system couldn't have accommodated millions of new claimants overnight, and arguably doesn't pay enough to keep a substantial chunk of the population at home and quiescent anyway. Which again, is what lockdown was implemented to do. It has to be not just enough to keep body and soul together, which let's be honest the benefits system doesn't necessarily provide anyway, but also enough to make sure the recipients are observing lockdown. That doesn't come cheap.