When I place a bet, I can estimate my edge because the outcome is binary. When the outcome is continuous, it is far more tricky. It is like saying a kid who learns to ride his trike is ready for MotoGP...they are just totally different.
And yes Soros put on big bets, but what you are missing with Soros is the fact that his hit rate was still 30%. Most of the stuff he did didn't work out, macro is largely bets on skewness not returns. Buffett had a higher hit rate but trying to suggest someone optimise a strategy based on what literally the best investor of all time did is...not smart. Even if you were better than Buffett, you might not be lucky.
The reason why Kelly doesn't work with value investing in particular is because your returns are largely random, you know that your portfolio has an edge but you don't usually know which position is going to revalue.
The reason why Kelly doesn't work with long-short in particular is because you aren't only betting on return but correlation. Anyone who runs Kelly will eventually get a correlation spike and blow up (this is also roughly true of macro, again why Soros isn't a good example, he largely bet on skewness).
I was a "pro" so I am also aware of what most pros do. Again, investors don't only look at return, they have to look at correlation, volatility (note that if you are betting on sports, you don't have to worry about things like correlation).