A "one-trick pony" school of game design would have to work along the lines of something even more reductive than, say, Scott Games' "Five Nights at Freddy's" series.
Imagine a similar series of games, where the only thing that changes from title to title is the art direction. The mechanics stay exactly the same, the responsiveness stays the same - maybe bug fixes would be implemented if we were lucky, but that's it. That would be a good example of "one trick pony"-esque design. FNaF avoids that pitfall because each entry mixes up your starting parameters, pushes you out of the comfort zone you sink in as soon as you've grasped the layout and mechanics of the previous title.
FromSoft isn't quite so calcified as to stick to one set of mechanics and never diverge from them. Their list of games has been brought up before, and a few titles they made didn't have anything in common with the Souls games. If anything, the Souls games are indicative of FromSoft finding a formula that works and tweaking it over several releases. If anything, Bloodborne is an extension of that effort. After the cautious approach that Dark Souls 1 and 2 fostered, the design team wanted to egg the players into a more aggressive mindset. They changed a few mechanics adequately, after confirming that they still had a solid foundation to work with.
If anything, the real offenders for a complete lack of innovation would have to be sports games licensors. Every new title isn't much more than a roster update with prettier graphics and the exact same control scheme, except when someone gets it in their minds to wedge in something that appeals to the tactician or the twitch gamer.
Captcha: Yellow-belly.
Yeah, that's what EA Sports is, basically. Afraid of breaking a formula that works, because its main audience isn't interested in gameplay, so much as the rote reproduction of what's on their TV screens every game night.