Clearly the difference was small. It sold better than its predecessor by a very large margin. If it had sold worse or sales numbers were notable lower than expected you'd have a point. But the market has spoken and it turns out they really don't care. This was the worst time to release on Epic as well. Once most of the useful features of Steam are added into it over the next few months are more AAA games come to the store there will be even less people actively avoiding it.
I still haven't seen anyone post proof of this. Do we have any proof of Out Worlds for example being paid to not sell on Steam? Or did the developer/publisher decide they'd sell on the store that has less fees? Some people seem to think offering lower costs = bribe.
You have no way of knowing what the difference was, I seem to recall the last game having a really rough launch with a lot of people requesting refunds and then eventually fixing most of the issues, that would setup a perfect scenario for this one to do much better at launch. There's a bunch of factors that go into how well a game sells(not to mention differences in how games sales have been counted over the years, especially with digital sales) and the only concrete thing we can take from this is that the game didn't flop due to the exclusivity.
This is from the linked article about him claiming the bribes were "procompetitive":
According to Sweeney, Valve has every right to negotiate free or exclusive distribution deals with developers and believes that companies choosing to partner together openly and exchange money or other benefits isn’t bribery.
That certainly doesn't sound like he's denying paying for exclusivity just that he's claiming it's not a bribe which much like his "procompetitive" claims are 100% horse shit from where I'm sitting.