It is completely normal, that the private-sale round has slightly lower prices then the public sale round, that is the benefit the big investors and VC's get for funding the project very early on where there is still a lot of uncertainty if the project can deliver. Of course though a 75% discount compared to the public sale is just way to much in my opinion because that way it is inevitable that massive dump happens as soon as the tokens are tradeable. Usually private sale tokens are not released all at once but according to a vesting schedule but it is not unusual that, like 10% of the private sale is unlocked on day 1 of trading and the rest is unlocked over the next year or so. So i would never participate in a public sale where i know that the private round was 75% cheaper.