Can we get higher internet speeds even with low BW message signals?
The concept you are searching for is called channel capacity.  If you do a web search on that term you should find a lot of information.

Basically, the capacity of a channel is determined by it's bandwidth, noise level, and the power you can put into your signal.  Theoretically, if I could only send one symbol per second I could still achieve 1Mbps as long as the noise was low enough to distinguish gradiations in the signal of \$10^{-6}\$.  OTOH, a 1MHz wide channel with so much noise that I could only send binary signals could also achieve that speed.

The "truth" is always somewhere in the middle, and provides a continual challenge for communications engineers to get more speed for less money on existing channels.