Attention-grabbing headline, but the article itself answers the question: very important.
"Hastings was one of those battles which changed the course of history, most directly for England but also, as events turned out, for Britain and for France... In terms of its consequences, Hastings must be the most important battle ever to have been fought in England... the consequences of its outcome changed the course of English history definitively."
"Hastings was one of those battles which changed the course of history, most directly for England but also, as events turned out, for Britain and for France... In terms of its consequences, Hastings must be the most important battle ever to have been fought in England... the consequences of its outcome changed the course of English history definitively."