In reality, airlines have the ability to hedge against (too) rapidly changing fuel/oil prices and they have a lot of smart people doing that
Since this mechanism does not exist in Airlinesim (for obvious reasons), I would at least suggest a limit on possible price increases/decreases, so that also fast changes are flattened and players can react without needing a lot of money or RL time at once
whether it’s a challenge or not depends a lot on the server situation (already collapsing demand?) and also on whether the airlines maintain (almost) local monopolies and thus achiving higher margins or whether the airlines are sitting on piles of cash on old servers and so on