I agree. They have more than a few future contenders (like Umar Nurmagomedov) and action fighters (Brandon Royval), but they get buried on the prelims while a loudmouth like Strickland gets to headline card after card so that everyone can see a 25 minute sparring session.
Being a good promoter doesn't mean taking popular fighters and capitalizing on their growing fame - it means taking an unknown but promising fighter and introducing him/her to the masses. But the UFC is not willing to put in that hard work - they keep going for low-hanging fruit like Greg Hardy / Paddy and hope that their "edgy" personas somehow translate into MMA success and crossover appeal. When it inevitably doesn't, UFC moves on to the next gimmick - the teenager Rosas, the Meatball Molly, etc.
Someone like Canelo or Fedor don't speak a word of English, haven't said or done anything outlandish / attention-grabbing in the media, but had the right team around them to propel them into global superstardom in their respective sports. It didn't happen overnight, but it has paid enormous dividends. UFC wants to take the easy road - take a loudmouth who won a few fights and cash in quickly, instead of investing long-term for a future payoff. Sure, it could be the fear that a fighter will become larger than the organization (like Conor did), but I feel it's less an issue of fear and more an issue of complacency.