Unfortunatelly DMA is the reason Google is doing this. It allowed Apple to require notarization for "security". Google is just copying the same approach as it's now clear what the requirements by the governments are.
Before it was unclear so it was better to allow installation of apps without any verification to appear as more open.
Remember any regulation/law has unintended consequences. At one point Apple decided that PWAs would no longer be supported in EU so they don't have to provide equal capabilities to implement them in alternative web browsers, fortunatelly they changed their mind by obtaining an exception. PWAs is the only alternative choice for making "proper" apps on iOS (no hacky sideloading methods).
I think overally DMA is more a loss than a win (good on paper, terrible in practice). It codified worse things. The EU app stores are still fully controlled by Apple (harder to install, they can just decline or drag notarization of any apps or revoke your license to dev tools, you need to still pay them, etc.).
For various apps the EU market is too small (esp. for things that need to be global) to invest into the development so while you can for example theoretically develop a real alternative web browser to Safari/WebKit (forbidden by App Store rules) nobody is willing to do it.