You're mixing certain numbers up. $500m was Endgame's approximate profit from its box office run, it will be much more in total.*Facepalm*
Infinity War's total profit was $500m, and that was based off $900m box office returns for the studio. Endgame's returns are $300m higher, and the movies were made together, with the cost for each essentially being equal, about half of a big total. So if you assume costs were the same as for IW, then Endgame is heading for $800m+ profit.
Now, perhaps there is a bigger budget on Endgame for various reasons, but I think that's counterracted by the fact that Endgame is setting home entertainment records, and TV deals will be super favourable for the new biggest film ever. Endgame's profit should be at the very least $700m.
I did. Ouch.
I have no idea how I made that mistake