I don't know if the OP post is true-- or partly true-- but to explain how it might be good for SoftBank: This was an all share deal, so sandbagging the value of Sprint shares so you can merge with TMobile could be good in the long run because you own shares in the new entity which has much less competition.
I'm not sure if SoftBank deserves the credit of assuming that their actions are based on sound logical reasoning.
They want to spend whatever billions it costs to consolidate the industry and then reap the monopolized profits down the road.