Ok so with my Lawyer hat on I took a quick look at the Zcash FAQ.
Zcash try to address the "premine" accusation, which is often seen as deleterious in the crypto community,
Zcash argument is effecitvely allocating funds after mining has started and open to anyone to mine, (semantically) Zcash then say it is "not a premine".
However materially it is the same thing.
The aspect of the premine in issue is not when the mining was done, but how a percentage of funds was always locked up, requiring everyone else to come on board and pick up the tab, give it value etc.
So it is disingenuous of Zcash to claim its not a premine while achieving exactly the same thing.
In effect they have extend/changed the temporal horizon of the premine to a postmine for 4 years.
How do you feel about a 4 year premine, well that's what you have here, a 4 year postmine
I am not saying a postmine is intrinsically wrong (or a premine for that matter), but I am saying they should be more transparent in their info to the community, if they wish to generate trust.
It cost money to develop the coin. If the price of the ZCash is very high, I do not mind them taking 20% share.