When stern was the only company still making games, that was a monopoly. A monopoly literally means one entity owning the market.
Now, there is a significant departure from being a monopoly with 5 major manufacturers who are competing against each other (stern, JJP, spooky, AP, CGC) and a few other smaller ones (DP, homepin, haggis, multimorphic, pinball bros), plus various homebrew innovators. Honestly, we have quite a wide range of options and ideas right now. I might go as far as to say that this resurgence is the second golden age of pinball.
Each manufacturer has tried different and unique things. JJP was the first to make a modern game with an LCD screen. Stern was the last manufacturer to follow that paradigm shift in display technology.
Spooky took a step back and did a street level game (TNA) from a homebrew designer, which was a huge hit, and quite different than what everyone else was doing at the time. Then stern started looking to the homebrew community for new talent & ideas, making a splash with Iron Maiden.
CGC brought back some beloved classics of the WPC era on a new platform with some added bells & whistles.
Multimorphic did something completely different with a screen as a playfield and swappable game modules. Regardless of what some people think about a screen vs playfield, that platform is quite a great innovation.
Sure, there have been many complaints about stern's cost cutting measures, from empty playfields, to paddle targets, to cabinet and playfield issues.
As for price, I think JJP has been blazing the price ceiling trail with their collector edition games.
If anything, I'd say having all the other manufacturers around is forcing stern to innovate and remain competitive.
Theme choices, game platforms, game code, mechs, layouts, artists and artwork, sounds & music--no one company is just cranking out cookie cutter cornerstone games that are lackluster or clones of previous games.