The argument is flawed.
It is cheaper to tear down Blk 20 and Blk 21 and acquired the piece of land that is as big as those occupied by the other 6 blocks (2 point blocks, 4 slab blocks).
Why tear down 6 blocks and not just 2 blocks?
By tearing down the 6 blocks, they need to tear down the community club and the Buona Vista HDB branch office as well, in order to settle the affected residents.
HDB should consider the big piece of land nearby (vacated by SERS Blk19 and Blk1

Blk20 and Blk21, when it went back to the drawing table last month. That piece of land is just as exclusive. It is not fair to just solely compute the sums based only on the land areas occupied by Blk20 and Blk21.
HDB should have revamped the Holland Drive SERS, rather than just simply consider a replacement block currently occupied by Blk20 and Blk21.
I'm not sure if MUP is their next best alternative. MUP had already lost its charm. Just look across the road, they would know that Blk 2 and Blk 4 still undergoing upgrading since 2002!
FYI, the worker party is working on the ground last Sunday. Saw them selling the hammers in Holland Drive and Ghim Moh markets. Why not, the GRC has not been contested for 2 terms, and none of the MPs (except Mr Teo Ho Pin) had ever contested. Moreover we have ministers who supported the integrated resorts. And having so many localised issues, the transport woes in Bukit Panjang, the unhapiness over SERS and upgrading progress, I am curious to know the support level here.
For those who had followed the story, HDB argued that all options have been considered:
a. Build 40 storeys with 6 units per floor, or
b. Build 40 storeys with 8 units per floor, or
c. Build 40 storeys with underground carpark, or
d. Sold the piece of land to private developers.
None of the above options enable HDB to recover the sums and compensations to Blk20 and Blk21 residents.
But shouldn't HDB consider:
a. the losses (close to 100k) per household?
b. the inconveniences suffered by the residents?
c. the intangible gains in higher selling prices for the new flats? Having 2 old blocks spoit the sights.
As what the residents may have observed, the authorities just (fu1 yan3 liao3 shi4). Allowing the residents to go to the media, having the HDB to return to the drawing table, having a closed door meeting with MP, ultimately they may be disgusted by the facts that the affected residents pressured them with media intervention. Heeding their suggestions may only open flood gate for more other precincts doing the same thing (what Mr Lim had mentioned).