Their goal isn't to run Steam out of business. And disagree either way. Waiting until you have feature parity before you launch of overly investing in a bunch of developers to get as much as you can out at launch is overly expensive, risky and can is inefficient. You basically have a bunch of people stepping on each other toes and being blocked waiting for others to get stuff done. The expression in development that's throw around is "9 women can't make a baby in one month". From a business perspective Epic is not going to wait yeras to get feature parity. When they already have the minimum needed to get people to use the service. Over time, they can expand organically and build out teams to implement features faster and faster. Many of the features not there are not that important to most players.
Either way Epic didn't have that much money back then and Tencent is only a part owner. They aren't going to put cash into a business they partly own without getting things out of it. Lets say they are full owner, it doesn't mean much to have more overall becasue most of it will never go to gaming. Just like Microosft having more money than Sony doesn't mean much because Microsoft isn't going to put all their eggs in their worst performing basket. Just like Tencent is going to put all their eggs in the risky new basket. When companies spend moeny, they don't think well if all this money gets burnt at least I still have this other money here. They spend on how much money they want to risk for a given project not how much excess they have.