They allow you to project power, as the saying goes, anywhere in the world, for extended durations, without needing the permission or assistance of any friendly nation (i.e. airstrips in a nearby country) [0].

If you're going up against any nation that doesn't have the ability to sink an aircraft carrier (which is almost every nation in the world) they are very far indeed from obsolete.

[0] So long as you have a serious logistics chain and serious support vessels including protective warships; if all you actually have is one aircraft carrier, you're going to find it pretty useless for long-term power projection.

The goal might be to deter and project power on lesser military capable nations than Russia or China (e.g. nations in Africa)

Indeed.

The defense against Russia and China is the nuclear deterrent. There is not going to be any direct war between France (or the West for that matter) and Russia/China.

I don't know about the French Navy but the US Navy has long had mature and adequate defenses against supersonic missiles. The US has been iterating on that kind of defense tech since the 1980s and has been a regular part of their planning.

OP probably meant hypersonics, of which USN / everyone else has no current defenses against. TLDR of a recent panel on state of anti-hypersonics is Pentagon hopes to have a "workable" defense against hypersonics by mid-2020s.

How many rods from god can SpaceX loft at a time?

Make those missiles [semi-]autonomous, and they're swarms of suicide drones:

https://www.jewishpress.com/indepth/opinions/firefly-israels...

I've heard people say that this obsoletes large surface vessels and even manned fighters.

They aren’t there to project power directly at other big military powerhouses.

They’re used to project power indirectly, by proxy wars in less developed countries (and sometimes for direct wars with them, without proxy of other empires, at least at start).

I think guiding a hypersonic glider on a moving target is a difficult task. I thought waves could not penetrate the plasma around the glider, making the last phase of the flight unguided ?