I’m repeating myself here, but it’s important. Web-based clients have always been a bad idea. Let’s Encrypt have consistently said they’re a bad idea. They’ve always been completely incompatible with the way Let’s Encrypt is designed to work, which is why LE have refused to develop one themselves. Not to mention the security concerns (it can be done securely, but most users won’t be able to verity that), and the fact that you’re at the mercy of yet another third party who can change the deal whenever they choose (which seems to have happened here).
So the most popular web client has suddenly become much less usable. This is a good thing. The appropriate response to this is not “build another web client,” but to stop using the web client and instead use Let’s Encrypt as it was intended to be used.