I don't fully get it.

The NWC layer means user just connect other wallets for redundancy when one wallet is offline?

But that makes them hold different amounts on different wallets, no?

This would cause lots of problems, users need to onboard to other wallets first, difficulties in UX in displaying balances (or one balance), problems with payments where your one NWC string has not enough bitcoin to pay something, even though you total balance shows you should, etc

But I am not sure If I understand your solution well

Another thing to mitigate those centralised APIs for nodeless wallets is for them is to just use Nostr 😉