You assume that Amazon has to use a US launch provider which isn’t the case.
So far there are at least five "maybes" in the equation:
1. amazon launching from Russia in large numbers 2. Khrunichev lowering the price of a single Angara significantly 3. Khrunichev being able to produce enough rockets in the first place 4. amazon being able to stack their satellites into the Angara 5. amazon being able to produce enough working satellites in the remaining time frame.
For me that still counts as vaporware.
If Starlink can't beat Kupier they're dead anyway those satellites will go up eventually.
That's not really the point though. Amazon is a fierce (and many times dirty) competitor to be up against.
If you're competing directly with AWS then you need to take every advantage you can get. If you're trying to build a global satellite network to provide internet access and not having launch capabilities will delay AWS long enough to get a foothold in the market then you take it.
I suppose {sat -> orbital DC -> sat} (latency) or {sat -> orbital DC processing -> ground} (transmission bandwidth) are the primary use cases? Maybe security?