No, you don't simply "move to a new coin". ETH is currently a 420B market cap and rewards GPU miners something on the order of 13,000 ETH a day conservatively (without fees). That's nearly 50m dollars a day or 1.5B dollars a month!

The only "other coins" available to be mined with GPUs are tiny. Ethereum classic has only a 8B market cap, Ravencoin with 1B, then many sub 1B coins.

https://www.kryptex.org/en/mining-calculator

What information do you have to backup that opinion?

As ETH is the biggest ship in the sea by far, they'll flood those other coins and subdivide a much smaller remaining market.