It may not be so much about assuming a discount, as it is about understanding that it is highly unlikely that the same buyer for3 waterfront properties and 2 additional houses, all sold together for a total of 5 homes bulk, is in any way the same owner buyer for one of the individual properties
I a single house purchase, a buyer can get financing, this type of bulk sale is usually cash or a specialty loan. Even if they pay cash, a buyer for one of the SFR waterfront homes might pay 550k, in a bulk sale the package might be 2 million $( or whatever it is )
Generally, an investment buyer which is the likely buyer for a bulk purchase expects some kind of return, including if they buy in bulk with the view of then splitting the properties up and putting the houses back on the market as 5 individual homes.