Indeed. The "market price" is really the "marginal price" of moving a share, not the average price over all shares.
(For something you actually want to consume or corner, usually, if you buy 99.9% of all shares of something, the price of the lat 0.1% will be quite high. But if the market is frothy and people are bidding up shares irrationally/temporarily, while many others are just holding old shares and not paying attention, then the average price--once the excess buy-side money is spent, and there isn't excess cash available to bid for more shares-- will be lower
(For something you actually want to consume or corner, usually, if you buy 99.9% of all shares of something, the price of the lat 0.1% will be quite high. But if the market is frothy and people are bidding up shares irrationally/temporarily, while many others are just holding old shares and not paying attention, then the average price--once the excess buy-side money is spent, and there isn't excess cash available to bid for more shares-- will be lower