If it really was the case that high risk startups were being systemically under valued such that an investment into YCombinator companies lead to greater returns than other investments, other market participants would have likely already exploited/corrected it.
This is often called the no arbitrage principle.
If someone invests into large companies it might indicate they hold the opinion that it swung too far in the opposite direction and the market is now overvaluing small companies relative to the large.
In this case SoftBank is specifically investing in Nvidia instead of a segment at large indicating they likely hold a very specific opinion. It probably wouldn't be correct to use this to say anything on their opinion to the value of something like YCombinator.
If it really was the case that high risk startups were being systemically under valued such that an investment into YCombinator companies lead to greater returns than other investments, other market participants would have likely already exploited/corrected it.
This is often called the no arbitrage principle.
If someone invests into large companies it might indicate they hold the opinion that it swung too far in the opposite direction and the market is now overvaluing small companies relative to the large.
In this case SoftBank is specifically investing in Nvidia instead of a segment at large indicating they likely hold a very specific opinion. It probably wouldn't be correct to use this to say anything on their opinion to the value of something like YCombinator.