In the future fees will account for more and more percentage of mining rewards, and this is the only way it can really work. Blockchain space will always be limited so people can donate spare resources of their home PC's to ensure decentralization of Bitcoin's network, so onchain transaction fees will be high - easily hundreds or thousands of dollars, and onchain transactions will be used for moving only big amounts of value. Small transactions will happen on higher layers like LN or on sidechains or whatever other cool solutions people will come up with. Onchain fees will always be fair because users will be essentially buying access to the most secure and trustless value transfer system in the world due to miners PoW - without sufficient PoW the system wouldn't be able to sustain past certain amounts of value, because it would become lucrative to attack it.

Alternative solution would be to increase blocksize to gigabytes, so fees will be cheaper but their sum would still buy enough PoW, but that would mean that there will be just a few full nodes in the world that can be very easily attacked by governments or can use their power to enforce whatever rules they like.

You could also remove 21mil cap to keep subsidizing PoW with mining rewards forever, but this would remove a lot of value from Bitcoin, which in the end might net less PoW than any of previous solutions.