You do not need an unpruned node to use the personal server. I've used it
with no problems on pruned nodes as small as 5gb
Are you sure? Transaction details would gone after the block is deleted and thus Electrum can't verify the integrity of the transaction from your local server.
Even if assuming there's way to "trust" a server and don't verify the integrity, all users could do is set of UTXO/input.
Edit : Thanks for the information, HCP