Instead it could appear if we have an old HODLer, who has not touched his coins nor synced any wallet in years, and then wants to transfer them.
1. If someone has some old wallet, then that person usually also can see some old transactions, even if it is SPV wallet.
2. If new coins were sent in the meantime, then without syncing the node, the owner does not know, if he received anything at all. Because online sites like block explorers can lie. And if the owner would sync even some SPV wallet, then he would get transactions in plaintext.
If he isn't able to connect to an archival node who has stored the whole blockchain, or alternatively the UTXO set, he wouldn't be able to move the coins.
That would happen only in case of "walletless" people, who just trust, that block explorers, and other online sites, are telling the truth. But in that case, they could be easily robbed anyway, because if a given block explorer would display some fake SHA-256 hash, and that would be signed with the real keys, then coins could be easily stolen in many cases, because a valid signature for a fake transaction, could be used in other contexts, to trigger some unexpected conditions.
it's a scenario where even true full nodes are scarce and most nodes are pruned
It is inevitable. If you count, how many pruned nodes are there, and compare it with the number of "nodeless" users, then I think the majority is not running any node at all. A lot of users are using SPV wallets, many users use exchanges, and never touch any on-chain coins, and now, more and more users are trading things like CFDs, where they don't have to touch any crypto, and where everything can be fake.
Also, if you think about it, and count, how many UTXOs can be created and consumed per block, then you will notice, that if Bitcoin would be adopted globally, then one UTXO per user is not a realistic scenario. It is very likely, that if people would want to globally use Bitcoin, then there would be thousands, millions, or more users, committed to a single UTXO. Which also means, that regular users would need many SPV-like merkle trees, to locate their coins on-chain. Now, LN assumes two users per UTXO, but this number is quite low, and it is not enough to onboard everyone.