Being able to run cross-platform browsers on iOS does in fact make the very thing you're complaining about better.
I would love it if the EU did in fact force apple to release a cross-platform iOS emulator to allow web developers to properly test iOS browsers, but presumably apple would argue that there are strong technical reasons there (and the DMA differentiates real technical reasons from monopolistic arbitrary roadblocks).
For making browsers available across regions, that's very obviously not driven by strong technical reasons. Making cross-platform code has real technical burden.