You run under the assumption that Epic is going to moneyhat games forever. Simply put, they are almost certainly not making a positive return on moneyhatting these games. The only reason they are currently doing it is that they cannot compete with Steam without exclusive games. Even if they had complete feature parity people would still use Steam because Steam is the established market leader. You have always bought games from Steam so unless something drastic happens you are going to keep buying from Steam. That isn't to pat Valve on the back, that is just the nature of consumers.
Epic is using exclusivity to actually carve out a marketshare in a ridiculously competitive market.
At a certain point, they are going to stop doing it because Steam isn't going away and they(Epic) are a business. Businesses exist to make money and buying exclusivity isn't profitable, it is just part of the start-up costs of gaining marketshare. Epic is hitting Valve in a meaningful way and Valve is eventually going to have to respond. What that response is, I have no clue. However, as someone who is very frustrated with Valve over their direction to let algorithms dictate user experience and champion GaaS over single player experiences, I want Valve to do something.
If that means something user-facing, then great. Maybe it will be Valve's own suite of exclusive games that wouldn't have otherwise existed. If it is developer-facing only, then good for them, better financial terms for developers will allow easier profitability and make it easier for them to succeed in the PC gaming market. If it is easier for developers to succeed in the PC market then that means more developers will enter the space and that means more games for us. Even if that doesn't happen (more games), better terms might allow developers to survive who would have otherwise folded.