That is what the Voltec drive train does. The gas engine only directly powers the wheels in some narrow range of conditions, and I challenge you to tell when. It feels 99% like a BEV driving experience.

How is that better?

The Volt was able to use the ICE to improve peak output directly, with fewer drivetrain losses.

e-power is a cost saving measure, not an advancement

A problem with most approaches to having the ICE drive the wheels to is that you don't run the ICE at it's most efficient setting. You gain in the drivetrain, but lose in the actual combustion. Whether you lose more in one than you gain in the other is an issue.

Except Voltec was also able to run the ICE at its most efficient setting by switching to Serial hybrid mode, where it was acting like the e-Power mode.

Voltec was using clutches to let you run like either the e-Power example or the Prius example on the fly, or even somewhere in between with the 2nd generation depending on power demands: https://gmauthority.com/blog/2015/02/secrets-of-the-2016-che...

CS3 is what you're describing when talking about the most efficient ICE operation