Yes you are correct that was that meta with top lane being far slower and we are talking about right now with the current meta.
With the meta that top has formed into in the past two years top zac would not be viable in any way shape or form.
If you cannot duel you are not viable and in order to make zac viable top his numbers would have to be so good jungle zac would be over powered.
This is because his power budget is heavily into initiating and disruption.
As well zac top was insane when his blobs did not go in the direction of his lane opponent and the heal was absolutely insane a time you must not have been present.
Can you provide those winrate numbers because I remember them far differently.
I have played zac even before he did not get cooldown reduction for w on blob pickup and before champions dropped extra blobs.