He is no longer active in trading. He is an old man. Quantum is a family fund these days run by those Soros has hired. Soros remains active on the World stage as one of the most consequential philanthropists. He founded the "Open Society Foundation" (Which see.)
More Soros than Simons, because Jim Simons was only the man who hired the right people surrounding him. With some of the proper employees they built that strategy, without input from outside Jim Simons would have never achieved that results. He just was the owner of his fund, that's it when you read the book from him. This is totally different when it comes to Soros because he was/is a great Macro trader himself. His employees are just kind of assist for him and nothing more.
In Simons book it is also clear the main trading idea until today was brought from an employee of Morgan Stanley where they had some very good years until it stopped working for them then they got hired from Simons. There they could not make it to work because of transaction costs. At that time also Simons and his employees were looking for intraday seasonalities on the 5min timeframe, which is just bullshit, as there is no such fine seasonality to be found. I can admit this because I have it backtested too some years ago. It is just pure overoptimisation and curve fitting and nothing else. So the main edge was brought by his additional employees also from IBM for very good programmers to minimize transaction costs. That is their main advantage or edge. It is minimizing market impact when they enter and exit a position based on the strategy from Morgan Stanley trader. I also could easily imagine that those programmers who were than alone in their group with no very good traders that they did not look around on other similar very good strategies. So it is just the simple and pure strategy brought from one trader who was in the Morgan Stanley group and then also got fired by Simons in just a few years. His other employees were no traders just pure programmers, but one of the very best ones in their subject. So all in all it is about level2 and orderbook data and optimization to minimize transaction cost. That is their advantage I would say, of course with the basic strategy behind. There might be some variations with that brought strategy from one trader, but I am guessing they did not play with other strategies surrounding the original one too much, because the other employees were just programmers and no traders. Until today they only hired Phds in hard subject and not mainly excellent traders with new strategy ideas. That might be also a reason why their AUM is capped at $10 billion for many years now, as they cannot trade bigger size without harming performance too much (with that one finetuned strategy 'only').
One could also say that the capability of Soros strategy is much higher in multiple times than Simons $10 billion strategy. Of course the sharpe may be higher on Simon, but there are several market makers who have also double digit sharpes so higher sharpe ratios than Simons. So I would say the greatest also means the highest absolute gain one can achieve, which is clearly Soros with his macro trading style on larger trends. There one could easily employ several hundred billions in positions. Simons could never do that. And of course the market makers are again smaller (with just hunting for the next tick(s)) but with highest possible Sharpe.
If you want the only edge from Jim Simons was that he is reputable math expert, who was able to hire also reputable IT experts. Without having that reputation it might be difficult to hire his IT experts he got. But this is all about perfectioning a working strategy, that is all what his programmers could achieve. It is not about idea creation, as there is and was no input from Simons and his programmers. Only a few traders in the past brought some ideas, that's it. And they stopped hiring excellent traders with new strategy ideas, what I do not understand as they are capped on $10 billion AUM for many years now. Simons has a strong favor to Phds in hard subjects and not for real traders. That might explain it. So basically they were just silent for decades because they only had ONE working strategy which they perfectioned it, nothing more. That is also a reason why the other funds of Jim Simons outside the Medallion were so poor in their performance because they were never looking for good traders. Their expertise is only in Math & IT, which is not enough for strategy idea creation (of course).
As Soros showed us it is the understanding of the markets where the edges come from and not the Math & coding thing.
If you go back over time scale then the greatest trader of all time could also be Jakob Fugger and the Rothschilds some centuries ago (being merchants or kind of traders). At that time they were huge to world GDP output in relation.
People who made wars do not count as traders I would say, because you cannot say a war is a kind of trade. They also forced other people to pay taxes, which is against the free will of any trade(s). The richest of all times was Emperor Augustus Caesar with ca. $4.6 trillion or 30% of worldwide GDP to that time. On Mansa Musa of Mali it is not know how much wealth he had under control. But these are clearly not the greatest trader of all time.