The Vision Fund is, among other things, the manifestation of the idea that an order of magnitude more scale will qualitatively change VC investing.
VC funds historically have been in the hundreds of millions, so you can invest up to tens of millions in any one company to keep a balanced portfolio.
SoftBank's Vision is in the hundreds of billions, so it can invest up to hundreds of millions.
This means they can single-handedly shepherd companies across the 'valley of death' or out-spend the competition to reach critical network effects... Essentially instead of just making bets, they're tipping the scales.
The point of this strategy is the scale, which is only possible by raising billions from sovereign wealth funds and mega corporations.
No one company could do it. Apple's net income last year was ~$60 billion.
The Vision Fund launched with $100 billion.