I think it can be a good thing the Ravencoin's halving, if the price goes up it can easily compensate the halving.
All the other proof of work blockchain minable with GPUs are very small blockchains compared to Ethereum blockchain. When ETH will be proof of stake you will see all the hash rate get distributed and moving regularly from one PoW coin to the others but yea I'm pretty sure the profit will never be the same.
My bro is a software engineer working for a DeFi company and he explained to me lately the latest developments in the Ethereum world and frankly these PoW coins like Ergo, Ravencoin etc. are simply not in the train in terms of future technology. Almost everything is happening on Ethereum blockchain (lately it's the Layer 2), the PoW coins are simple investment investment vehicles. Even Ergo doesn't have a lot of resources for coders, the vast majority of developers are on Ethereum.
Cardano coming soon will be interesting to follow!