“One antisemite is one too many, but the scale of the problem was also dramatically overstated for political reasons by our opponents inside and outside the party, as well as by much of the media. That combination hurt Jewish people and must never be repeated.
Was it overstated by amplified inside the party?

Luciana Berger, MP: "“I call a spade a spade. If someone themselves makes anti-Semitic comments, if someone themselves shares a platform with anti-Semites, they’re anti-Semitic.”

Was it weaponized by opponents outside the party?

Undoubtedly. There was a report on the Tory party conference having a panel about Islamaphobia where each question selected from the audience was about anti-Semitism in the Labour party. Every slightest thing, wearing a crooked tie for example despite now supporting a prime minister who deliberately messes his hair up before TV appearances, was weaponised against Corbyn. Heck, Corbyn was mocked for wearing a green tie by Tory MP's so May had to quickly tell them it was an anniversary of the Grenfell fire.

Does that matter?

It can only be amplified, weaponised or overstated if there is something enough there, and Corbyn's response to it was inadequate. He was not/is not an anti-Semite but he did lack understanding, did lack leadership skills and, potentially because he felt obstructed from his party let alone outside, he became firstly resistant to any criticism and then resistant and willing to awkwardly counterpunch which is how supporters of his then acted also, some of them without any restraint and some of who were certainly anti-Semitic. But in doing so that moved him and the party under him slightly so no longer could claim to oppose all racism and caused a lot of pain to innocent people.

Was yesterday the day to explain or defend his actions further?

No. He should have apologised but again showed a lack of leadership skills.

Was he all bad?

Not at all. Under Corbyn many Black, brown, LGBT+, poor, refugee, and disabled people felt politics truly cared about them for the first time. Corbyn only became leader because many people felt they had been pushed out from politics for too long and, despite a minority believing in Corbyn or his ability to deliver, the ideas he presented from a soft European left perspective were overwhelmingly popular when polled individually. I mean, in hindsight did we need internet access for all this year or pushing ahead haphazardly with Brexit? If Labour are to win real change then the ideas and some of his behaviour will have to be continued.