It's honestly not that big of a problem. Probably some anti-trust legislation can/should be passed to make installing F-Droid and the like easier, but it's already pretty easy. If enough popular apps start requiring you to install them through F-Droid then that'll become normalized and Google will lose its soft monopoly in this space, which is an outcome I'm all for.
Google is making it much more difficult and annoying to install F-Droid and any apps from there RIGHT NOW.
To the point where it will cease to be a viable way of distribution for any app that wants to attract an audience larger than the handful of power users.
There is no reason at all to defend them.