The way I learned it, is that people have a tendency to emphasize, so when became overwhelmed. You see the same thing with ‘good’, ‘great’, and 'epic’meaning the same thing within certain contexts.
If you want to get technical, I believe “whelm” originally came from waves hitting the hull of a ship, overwhelmed was when the waves crashed over the side and onto the deck.
Why can I be overwhelmed or underwhelmed, but not perfectly adequately whelmed?
Whelm and overwhelm are synonyms.
The way I learned it, is that people have a tendency to emphasize, so when became overwhelmed. You see the same thing with ‘good’, ‘great’, and 'epic’meaning the same thing within certain contexts.
If you want to get technical, I believe “whelm” originally came from waves hitting the hull of a ship, overwhelmed was when the waves crashed over the side and onto the deck.