I have never heard a fighter complain about getting "hard fights", they literally get paid to fight. As long as they give you enough time to prepare and is against someone in your same weight class, then that is a BS argument. Plus, if a fighter is worried about getting "very hard fights" then maybe they are not ready for the UFC, its not like the UFC will spoil you with easy fights. If the promotion cannot guarantee the fighters with at least 2 fights per year, than yes, that is not fair and should be looking for a way out, but if they are worried about "hard fights" or being "cannon fodder" then its a BS argument.
The UFC is notorious for giving BS fights in order to fuck with fighter's contracts, Gray Maynard, Josh Thomson, Lyotto Machida, Roy Nelson, Mark Hunt etc. have talked extensively about it. When your contract is about to expire and you dont want to re-sign they offer you a very short notice fight against someone outside your weight class and if you dont take it, then your contract extends for 2 more years, for example. Or they offer you a shit fight in the prelims and if you dont accept it they will shelf you and dont offer you another fight until the end of said contract. Every fighter's dream is the UFC but is not like once in the UFC is all peaches and plums and rainbows, they also have shitty business practices.
BTW, Chimaev is the exception, not the rule. He got 3 fights in 70 days but is not like every fighter gets to fight that much, the UFC roster is over 600 fighters, not everyone will fights more than 2 times a year; its just not possible.