So looking at that chart the fact it's winning out over the other variant is a given.
Is it causing more cases than would have otherwise been seen? Or is it replacing other variants?
The claims would suggest the former but then why has the number of cases involving previously known variants reduced so significantly?
Think of it as little fires in a field of straw. Each blade of straw is a person and the little fires are clusters of cases . These little fires usually burn themselves out, because the straw is generally quite sparse (lockdown/social distancing etc) unless a spark is thrown up and lands in a different patch of dense straw. When a spark lands in one of these patches, every blade that gets burned by the fire that spark starts will be the same variant as the spark that started it.
There’s two possible scenarios here.
One is that one of these sparks starts a particularly sparky fire, flinging sparks much further and more rapidly than usual. That will start more of these unusually sparky fires. And so on. Rinse and repeat.
The alternative scenario is that a spark lands in an area of the field where there is an unusually large patch of straw that is very closely packed together (a region where people are crap at social distancing) so the fire keeps spreading and spreading until you have a much larger fire than usual.
In both scenarios you end up with a single spark causing the majority of the burning straw at a given moment in time. One is a property of the spark, the other is a property of the straw.
Think I’ve torn the arse out of that analogy now but hopefully it makes sense!