The STAR award is likely higher than the host carrier one because you can get further. For example, just taking a LH award to NAmerica would limit you to that carrier's gateways, while the STAR award would permit a connection [with stopover?] onward to one of several hundred cities served by UA or AC. In that, it is akin to cashing in two separate awards, and thus still could represent a savings from the current charts.

The biggest problem until now for using STAR carriers on awards to Africa from NAmerica has been the need to take one award across the Atlantic, then another from Europe to Africa. This makes STAR much less competitive than oneworld. [I am sure similar situations exist from Europe to some destinations, as well as from Asia to others.]

My understanding is that each carrier still has its own program award chart for awards using just that carrier, but now there is a single STAR chart. But does this mean one is no longer able to redeem, say LH points, on just UA flights under an UA chart, or AC under an AC chart? I assume this will now be the case.