They don't solve much at all, other than blocking annoyances and improving the browsing experience.
The ads blocked by most adblockers is a tiny part of the advertising you are exposed to. It's also a great signal that shows that you are an "adblock user". Everything bit of data is used and you are not special or hard to reach.
They dont solve 'everything', but they solve quite a lot.
We can tell how effective they are, by how much many ad funded website complain about them.
Harm minimization is still a useful strategy.