Celestial clocks for telling the seasons, and locations for convergent gatherings ever X seasons. The megalithic stone structures at least. The smaller but more numerous wooden pole circles (horseshoe shaped really) were centers of local villages, the Neolithic equivalent of a fort or medieval castle.

Unless you can produce a very strong source that those solutions are now considered universally to be true, I don't think you can say that to be definitely so.

Firstly, looking at the actual henge, though the defence hypothesis is strong, there are several henges throughout the UK that lack the defensive structuring, but still take the right form, making it at least partly unlikely. Secondly, they seem to have been built away from population areas. Whilst a strong theory, it hasn't solved those problems, and so other solutions hold equal weight.

Secondly, the celestial clock theory is actually fairly weak. Only about half of the henges featuring large stonework actually line up with astronomical events, even when modeled for the timelines we think they were put in place for. Some might be reasoned to track stars, some mountains, and so on. It doesn't quite fit, especially as their north-offsets are very consistent.

You have some theories, which are popular theories, but so far as I'm aware, there are other equally popular theories held by the people in the field, and this isn't considered to be 'solved'.