I agree that it was unlikely that the shill accounts came from investors. If I created an alt with a couple partners I would have taken some of my own BTC and invested it across many shill accounts to make it appear that the distribution is greater than appeared. It is impossible to know an exact number. Minimum would be around 5 controlling over 50% stake and max 73. Our estimates of 5-9 is a very rough guess judging from initial blockchain distribution graphs (which were subsequently removed because they were far too granular.
https://nxtblocks.info/#section/blockexplorer_distribution shows a rougher approximation with the highest category being between 1 million and a billion where a previous breakdown reflecting only a handfull accounts between the 10 million and billion.
You are assuming that BCNext was a liar, cheater and thief. Imo, from what I have read, inquired and experienced this was not the case. I'd like anyone who believes otherwise to run a taint analysis on the NXT funding address. I think it is pretty obvious that BCNext was an idealist and not out to make as much money as possible by scamming others because he limited donations to 21 BTC.
Your belief of mining being more "fair" than a crowdsale is imo not accurate. With mining a currency, you are simply abstracting the crowdsale from the coin and sending your money to the hardware manufacturers and electricity providers. That doesn't make it more "fair". There will always be people with more money who can purchase more mining hardware and pay a larger electric bill.